Questions & Answers
ICSE - Grade - 10
Subject: Physics
Chapter - 04 - Refraction of Light
Types of Questions
MCQ
- Refraction occurs when light:
a) Bounces back
b) Changes direction in the same medium
c) Passes from one medium to another
d) Gets absorbed
Answer: c) Passes from one medium to another - Light bends towards the normal when it passes:
a) From air to vacuum
b) From rarer to denser medium
c) From denser to rarer medium
d) Through a mirror
Answer: b) From rarer to denser medium - Refractive index is defined as:
a) sin i / sin r
b) c × v
c) v / c
d) sin r / sin i
Answer: a) sin i / sin r - The speed of light is maximum in:
a) Water
b) Glass
c) Vacuum
d) Diamond
Answer: c) Vacuum - The unit of refractive index is:
a) m/s
b) No unit
c) cm
d) Hz
Answer: b) No unit - When light travels from glass to air, it:
a) Bends towards the normal
b) Slows down
c) Bends away from the normal
d) Gets absorbed
Answer: c) Bends away from the normal - Which law states that the incident ray, refracted ray, and normal lie in the same plane?
a) Newton’s law
b) Snell’s first law
c) Ohm’s law
d) Huygen’s law
Answer: b) Snell’s first law - Lateral shift is observed in:
a) Plane mirror
b) Convex lens
c) Rectangular glass slab
d) Concave mirror
Answer: c) Rectangular glass slab - What is the speed of light in water?
a) m/s
b) m/s
c) m/s
d) m/s
Answer: a) m/s - Refractive index
a)
b)
c)
d)
Answer: c) - Which phenomenon makes a stick appear bent in water?
a) Reflection
b) Dispersion
c) Refraction
d) Scattering
Answer: c) Refraction - The emergent ray in a glass slab is:
a) Deviated from its path
b) Reflected
c) Parallel to the incident ray
d) Perpendicular to the incident ray
Answer: c) Parallel to the incident ray - Apparent depth is always:
a) More than real depth
b) Equal to real depth
c) Less than real depth
d) Same as focal length
Answer: c) Less than real depth - The critical angle depends on:
a) Shape of prism
b) Colour of light
c) Refractive index
d) Temperature only
Answer: c) Refractive index - Total internal reflection occurs when light:
a) Travels from rarer to denser
b) Falls normally
c) Incidence angle > critical angle
d) Enters vacuum
Answer: c) Incidence angle > critical angle - Which device uses total internal reflection?
a) Concave mirror
b) Glass slab
c) Optical fibre
d) Plane mirror
Answer: c) Optical fibre - In TIR, the angle of refraction is:
a) 0°
b) Less than 90°
c) Equal to the critical angle
d) Not formed
Answer: d) Not formed - A prism deviates light:
a) Away from the base
b) Towards the base
c) Perpendicularly
d) Not at all
Answer: b) Towards the base - The minimum deviation occurs when:
a) Angle of incidence is zero
b) Angle of incidence is equal to angle of emergence
c) Light falls normally
d) Prism is absent
Answer: b) Angle of incidence is equal to angle of emergence - Formula for critical angle is:
a)
b)
c)
d)
Answer: b) - The i–δ curve shows:
a) Constant speed
b) Constant refraction
c) Variation of deviation with angle of incidence
d) No variation
Answer: c) Variation of deviation with angle of incidence - Which of these is NOT a condition for TIR?
a) Light from denser to rarer medium
b) Incidence angle < critical angle
c) Incidence angle > critical angle
d) Both media should be transparent
Answer: b) Incidence angle < critical angle - Speed of light in glass:
a) m/s
b) m/s
c) m/s
d) m/s
Answer: c) m/s - What is refracted when light enters obliquely?
a) Medium
b) Wavelength
c) Frequency
d) Direction
Answer: d) Direction - The refractive index of diamond is:
a) ~1.5
b) ~2.4
c) ~1.0
d) ~3.0
Answer: b) ~2.4 - Light travels fastest in:
a) Glass
b) Diamond
c) Air
d) Water
Answer: c) Air - Real depth ÷ Refractive index = ?
a) Speed
b) Apparent depth
c) Real height
d) Deviation
Answer: b) Apparent depth - The path of light is reversible. This is called:
a) Duality
b) Reflection
c) Reversibility principle
d) Newton’s law
Answer: c) Reversibility principle - Critical angle for glass-air is:
a) 42°
b) 60°
c) 90°
d) 30°
Answer: a) 42° - When i = 0°, r = ?
a) 0°
b) 90°
c) C
d) Depends on medium
Answer: a) 0° - Which ray is not bent?
a) Oblique incidence
b) At normal incidence
c) From glass to air
d) From air to water
Answer: b) At normal incidence - Deviation in prism increases when:
a) i decreases
b) i = 0°
c) i > 45°
d) i = 90°
Answer: c) i > 45° - Which device uses prisms?
a) Thermometer
b) Periscope
c) Barometer
d) Ammeter
Answer: b) Periscope - A prism splits white light due to:
a) Refraction
b) Reflection
c) Dispersion
d) Polarisation
Answer: c) Dispersion - The angle between refracting surfaces of a prism is:
a) Base angle
b) Critical angle
c) Angle of prism
d) Vertex angle
Answer: c) Angle of prism - Refraction is used in:
a) Electric circuits
b) Musical instruments
c) Optical instruments
d) Engines
Answer: c) Optical instruments - Which is denser?
a) Air
b) Water
c) Glass
d) Vacuum
Answer: c) Glass - Multiple images in thick mirror are due to:
a) Refraction
b) Dispersion
c) Repeated reflections
d) TIR
Answer: c) Repeated reflections - Which prism produces 180° deviation?
a) Equilateral prism
b) 30°-60°-90°
c) Right-angle prism
d) Cylindrical prism
Answer: c) Right-angle prism - Twinkling of stars is due to:
a) Rotation
b) TIR
c) Refraction
d) Eclipse
Answer: c) Refraction - Which medium has highest μ?
a) Glass
b) Air
c) Water
d) Diamond
Answer: d) Diamond - Lateral shift occurs in:
a) Concave mirror
b) Plane mirror
c) Rectangular glass block
d) Lens only
Answer: c) Rectangular glass block - In a prism, emergent ray is:
a) Undeviated
b) Parallel to incident ray
c) Bent from incident ray
d) Reflected
Answer: c) Bent from incident ray - μ = c/v indicates:
a) Faster light in medium
b) Slower light in vacuum
c) Medium slows down light
d) No refraction
Answer: c) Medium slows down light - Ray going undeviated means:
a) Normal incidence
b) TIR
c) Dispersion
d) Critical angle
Answer: a) Normal incidence - i = r when:
a) μ = 1
b) Angle of prism is zero
c) Same medium
d) Angle of incidence = 90°
Answer: c) Same medium - Use of erecting prism:
a) Make image upside down
b) Eliminate image
c) Make image erect
d) Rotate image
Answer: c) Make image erect - Mirages are caused by:
a) Plane mirrors
b) Water
c) Atmospheric refraction
d) TIR in glass
Answer: c) Atmospheric refraction - In right-angle prism, image deviation can be:
a) 60°
b) 90° or 180°
c) 30°
d) 0°
Answer: b) 90° or 180° - Apparent depth is used in:
a) Astronomy
b) Swimming pool observation
c) Satellites
d) Spectroscopy
Answer: b) Swimming pool observation
Fill in the Blanks
- Refraction is the ______ of light as it passes from one medium to another.
Answer: bending - The speed of light is maximum in ______.
Answer: vacuum - The refractive index , where c is the speed in ______.
Answer: vacuum - The unit of refractive index is ______.
Answer: no unit - Light bends ______ the normal when it passes from air to glass.
Answer: towards - Light bends ______ the normal when it goes from water to air.
Answer: away from - The angle of incidence and angle of refraction are related by ______ law.
Answer: Snell’s - The formula is known as ______.
Answer: Snell’s law - If the angle of incidence is zero, the angle of refraction is ______.
Answer: zero - The path of light is ______ according to the principle of reversibility.
Answer: reversible - The emergent ray in a glass slab is ______ to the incident ray.
Answer: parallel - The shift observed in a glass slab experiment is called ______ shift.
Answer: lateral - The speed of light in glass is approximately ______ m/s.
Answer: - The speed of light in water is approximately ______ m/s.
Answer: - The refractive index of a medium is always ______ than one.
Answer: greater - Refraction occurs due to a change in the ______ of light.
Answer: speed - Real depth ÷ refractive index = ______ depth.
Answer: apparent - A stick in water appears bent due to ______.
Answer: refraction - A prism is a transparent body with ______ surfaces.
Answer: polished - Light deviates ______ the base of a prism.
Answer: towards - Dispersion of light is observed using a ______.
Answer: prism - The curve between angle of incidence and deviation is called ______ curve.
Answer: i–δ - Total Internal Reflection occurs only when light travels from ______ to ______ medium.
Answer: denser, rarer - The angle of incidence for which angle of refraction becomes 90° is called ______.
Answer: critical angle - TIR takes place when the angle of incidence is ______ the critical angle.
Answer: greater than - The formula for critical angle is , where C is the ______.
Answer: critical angle - The phenomenon responsible for mirage formation is ______.
Answer: total internal reflection - ______ prisms are used in binoculars to reflect light.
Answer: Right-angle - Optical fibres work on the principle of ______.
Answer: total internal reflection - The twinkling of stars is due to ______ of light.
Answer: atmospheric refraction - In a thick mirror, multiple images are formed due to repeated ______.
Answer: reflections - The emergent ray in a rectangular glass block is ______ to the incident ray.
Answer: parallel - When light enters obliquely from one medium to another, its ______ changes.
Answer: direction - The ratio of real depth to apparent depth gives the ______.
Answer: refractive index - The phenomenon where light returns completely into the same medium is called ______.
Answer: total internal reflection - A prism has an angle between its two refracting surfaces called ______.
Answer: angle of prism - The deviation produced by a prism depends on its ______ and refractive index.
Answer: angle - A ray incident along the normal passes ______.
Answer: undeviated - In TIR, no ______ ray is formed.
Answer: refracted - Lateral shift increases with increase in ______ of glass slab.
Answer: thickness - The apparent depth is always ______ than the real depth.
Answer: less - A ______ prism gives 90° or 180° deviation.
Answer: right-angle - In a prism, angle of incidence = angle of emergence at ______ deviation.
Answer: minimum - Optical instruments use ______ to direct light internally.
Answer: prisms - The bending of light due to a change in medium is called ______.
Answer: refraction - When a light ray goes from denser to rarer medium, it bends ______ the normal.
Answer: away from - The image formed by TIR is brighter than that by ______.
Answer: reflection from mirror - The critical angle for glass-air is approximately ______.
Answer: 42° - Light travels in ______ lines in a homogeneous medium.
Answer: straight - Refractive index depends on the ______ of the media.
Answer: optical density
Name the Following
- The phenomenon of bending of light when it passes from one medium to another.
Answer: Refraction of light - The speed of light in vacuum.
Answer: 3 x 108 m/s - The device used to produce dispersion of white light.
Answer: Prism - The unit of refractive index.
Answer: No unit - The law that relates angle of incidence and angle of refraction.
Answer: Snell’s Law - The medium in which the speed of light is maximum.
Answer: Vacuum - The principle which states that the path of light is reversible.
Answer: Principle of reversibility of light - The formula for refractive index using speed.
Answer: μ = c / v - The ray that emerges from a glass slab after refraction.
Answer: Emergent ray - The shift observed in a glass slab experiment.
Answer: Lateral shift - The type of ray which bends towards the normal.
Answer: Refracted ray from rarer to denser medium - The optical illusion seen in deserts due to TIR.
Answer: Mirage - The bending of light towards base in a prism.
Answer: Deviation - The point of intersection of the extended incident and emergent ray in glass slab.
Answer: Lateral shift point - The device based on TIR used in binoculars.
Answer: Right-angle prism - The equation relating real depth and apparent depth.
Answer: Apparent depth = Real depth ÷ Refractive index - The angle between two refracting surfaces of a prism.
Answer: Angle of prism - The condition under which no refraction occurs.
Answer: Normal incidence - The phenomenon responsible for twinkling of stars.
Answer: Atmospheric refraction - The minimum angle of incidence for which angle of refraction is 90°.
Answer: Critical angle - The phenomenon that occurs when angle of incidence > critical angle.
Answer: Total internal reflection - The curve that shows variation of deviation with incidence angle.
Answer: i–δ curve - The principle behind optical fibre communication.
Answer: Total internal reflection - The image property changed by erecting prism.
Answer: Inverted image becomes erect - The speed of light in glass.
Answer: 2 x 108 m/s - The speed of light in water.
Answer: 2.25 x 108 m/s - The law that explains refraction through a glass block.
Answer: Snell’s Law - The ray which is incident at 0° angle.
Answer: Normally incident ray - The medium in which light travels slowest among vacuum, air, water, and glass.
Answer: Glass - The value of refractive index for air (approximately).
Answer: 1 - The phenomenon where emergent ray is parallel to incident ray.
Answer: Refraction through a glass slab - The effect observed when a stick partially in water appears bent.
Answer: Apparent bending due to refraction - The angle formed between incident ray and normal.
Answer: Angle of incidence - The angle formed between refracted ray and normal.
Answer: Angle of refraction - The method to determine refractive index of glass experimentally.
Answer: Using pins and protractor with glass slab - The mirror type where multiple images may be seen due to thickness.
Answer: Thick plane mirror - The prism type used to deviate light by 180°.
Answer: Right-angle prism - The diagram showing light passing through glass block.
Answer: Refraction diagram with lateral shift - The critical angle formula.
Answer: sin C = 1/μ - The property of light that remains unchanged in refraction.
Answer: Frequency - The name of the surface where incident light enters a prism.
Answer: Refracting face - The instrument where prisms are preferred over mirrors.
Answer: Periscope - The prism with angles 60°, 60°, and 60°.
Answer: Equilateral prism - The prism that gives less than 60° deviation.
Answer: 30°–60°–90° prism - The base angle in a prism where deviation occurs.
Answer: Prism base - The cause for formation of multiple images in thick glass.
Answer: Multiple internal reflections - The property of medium that determines refraction.
Answer: Optical density - The speed formula related to wavelength and frequency.
Answer: - The reason TIR gives brighter images than mirrors.
Answer: No light loss in TIR - The instrument using TIR to transmit light signals.
Answer: Optical fibre
Answer in One Word
- The bending of light as it enters a different medium.
Answer: Refraction - The point where the light enters a new medium.
Answer: Interface - The ray that changes direction in the second medium.
Answer: Refracted - The law governing the ratio of sines of angles.
Answer: Snell’s - A transparent object used to disperse light.
Answer: Prism - The speed of light is maximum in this medium.
Answer: Vacuum - The measure of how much light slows in a medium.
Answer: Refractive index - The angle formed with the normal in the first medium.
Answer: Incidence - The angle in the second medium.
Answer: Refraction - The shift seen in a glass slab experiment.
Answer: Lateral - The type of shift where the emergent ray is parallel.
Answer: Lateral - Light bends towards this when entering denser medium.
Answer: Normal - Light bends away from this when entering rarer medium.
Answer: Normal - Refraction does not occur when angle of incidence is.
Answer: Zero - The speed of light in glass (approx).
Answer: 2 x 108 m/s - The speed of light in water (approx).
Answer: 2.25 x 108 m/s - Light travels in this type of path in uniform medium.
Answer: Straight - The optical illusion formed in deserts.
Answer: Mirage - The medium with refractive index closest to 1.
Answer: Air - Principle stating light can reverse path.
Answer: Reversibility - The point where incident and emergent rays meet if extended.
Answer: Shift - The path light follows inside optical fibre.
Answer: Zigzag - Angle at which refraction is 90°.
Answer: Critical - Complete reflection within a denser medium.
Answer: Total Internal Reflection - Short form of Total Internal Reflection.
Answer: Total Internal Reflection - Rays beyond the critical angle get fully ______.
Answer: Reflected - The emergent ray from a glass slab is ______ to incident ray.
Answer: Parallel - Twinkling of stars is caused by this.
Answer: Refraction - Angle inside a prism between refracting surfaces.
Answer: Prism - Total Internal Reflection occurs only from ______ to rarer medium.
Answer: Denser - The colorless, transparent block used in labs.
Answer: Glass - Device that reflects light using Total Internal Reflection.
Answer: Prism - The shape of a prism base used in labs.
Answer: Triangular - Rays that do not deviate.
Answer: Normal - Symbol for refractive index.
Answer: μ - Unit of refractive index.
Answer: None - A medium with μ > 1 is called ______.
Answer: Denser - The fastest speed of light occurs in this.
Answer: Vacuum - The key phenomenon used in optical communication.
Answer: Total Internal Reflection - The practical demonstration of refraction uses this.
Answer: Glass slab - Light ray inside prism bends towards ______.
Answer: Base - The light component used in fibre optics.
Answer: Laser - A device using prism to create upright image.
Answer: Periscope - Light appears to bend at water surface because of ______.
Answer: Refraction - When μ = 1, light continues ______.
Answer: Undeviated - Apparent depth is always ______ than real depth.
Answer: Less - Snell’s law uses ______ of angles.
Answer: Sine - μ = sin i ÷ sin r is valid for ______ rays.
Answer: Oblique - Light always takes the path of least ______.
Answer: Time - A diagram showing deviation in prism.
Answer: Ray
ICSE - Grade 10 - Physics
All Chapters
- Chapter 1 – Force
- Chapter 2 – Work, Energy and Power
- Chapter 3 – Machines
- Chapter 4 – Refraction of Light at Plane Surfaces
- Chapter 5 – Refraction through Lens
- Chapter 6 – Spectrum
- Chapter 7 – Sound
- Chapter 8 – Current Electricity
- Chapter 9 – Electrical Power and Household Circuits
- Chapter 10 – Electro-magnetism
- Chapter 11 – Calorimetry
- Chapter 12 – Radioactivity
ICSE - Grade 10 - Chemistry
All Chapters
- Chapter 1 The Language of Chemistry
- Chapter 2 Chemical Changes and Reactions
- Chapter 3 Water
- Chapter 4 Atomic Structure and Chemical Bonding
- Chapter 5 The periodic table
- Chapter 6 Study of the first Element Hydrogen
- Chapter 7 Study of Gas laws
- Chapter 8 Atmospheric Pollution
ICSE - Grade 10 - Mathematics
All Chapters
- Chapter 1 Rational and Irrational Numbers
- Chapter 2 Compound Interest [Without Using Formula]
- Chapter 3 Compound Interest [Using Formula]
- Chapter 4 Expansions
- Chapter 5 Factorisation
- Chapter 6 Simultaneous Equations
- Chapter 7 Indices
- Chapter 8 Logarithms
- Chapter 9 Triangles
- Chapter 10 Isosceles Triangles
- Chapter 11 Inequalities
- Chapter 12 Midpoint and Its Converse
- Chapter 13 Pythagoras Theorem
- Chapter 14 Rectilinear Figures
- Chapter 15 Construction of Polygons
- Chapter 16 Area Theorems
- Chapter 17 Circle
- Chapter 18 Statistics
- Chapter 19 Mean and Median
- Chapter 20 Area and Perimeter of Plane Figures
- Chapter 21 Solids
- Chapter 22 Trigonometrical Ratios
- Chapter 23 Trigonometrical Ratios of Standard Angles
- Chapter 24 Solutions of Right Triangles
- Chapter 25 Complementary Angles
- Chapter 26 Coordinate Geometry
- Chapter 27 Graphical Solution
- Chapter 28 Distance Formula
ICSE - Grade 10 - Biology
All Chapters
- Chapter 1 Introducing Biology
- Chapter 2 Cell: The Unit Of Life
- Chapter 3 Tissues: Plant And Animal Tissue
- Chapter 4 The Flower
- Chapter 5 Pollination and Fertilization
- Chapter 6 Seeds: Structure and Germination
- Chapter 7 Respiration in Plants
- Chapter 8 Five Kingdom Classification
- Chapter 9 Economic Importance of Bacteria and Fungi
- Chapter 10 Nutrition
- Chapter 11 Digestive system
- Chapter 12 Skeleton: Movement and Locomotion
- Chapter 13 Skin: The Jack of all trades
- Chapter 14 The Respiratory System
- Chapter 15 Hygiene: [A key to Healthy Life]
- Chapter 16 Diseases: Cause and Control
- Chapter 17 Aids to Health
- Chapter 18 Health Organizations
- Chapter 19 Waste Generation and Management
ICSE - Grade 10 - History
All Chapters
- Chapter 1 – The Harappan Civilisation
- Chapter 2 – The Vedic Period
- Chapter 3 – Jainism and Buddhism
- Chapter 4 – The Mauryan Empire
- History — Chapter 5
The Sangam Age - Chapter 6 – The Age of the Guptas
- Chapter 7 – Medieval India — (A) The Cholas
- Chapter 8 – Medieval India — (B) The Delhi Sultanate
- Chapter 9 – Medieval India — (C) The Mughal Empire
- Chapter 10 – Medieval India — (D) Composite Culture
- Chapter 11 – The Modern Age in Europe — (A) Renaissance
- Chapter 12 – The Modern Age in Europe — (B) Reformation
- Chapter 13 – The Modern Age in Europe — (C) Industrial Revolution
ICSE - Grade 10 - Civics
All Chapters
- Chapter 1: Our Constitution
- Chapter 2: Salient Features of the Constitution — I
- Chapter 3: Salient Features of the
- Constitution — II
- Chapter 4: Elections
- Chapter 5: Local Self-Government — Rural
- Chapter 6: Local Self-Government — Urban
ICSE - Grade 10 - Geography
All Chapters
- Ch 1 – Earth as a Planet
Ch 2 – Geographic Grid: Latitudes and Longitudes
Ch 3 – Rotation and Revolution
Ch 4 – Earth’s Structure
Ch 5 – Landforms of the Earth
Ch 6 – Rocks
Ch 7 – Volcanoes
Ch 8 – Earthquakes
Ch 9 – Weathering
Ch 10 – Denudation
Ch 11 – Hydrosphere
Ch 12 – Composition and Structure of the Atmosphere
Ch 13 – Insolation
Ch 14 – Atmospheric Pressure and Winds
Ch 15 – Humidity
Ch 16 – Pollution
Ch 17 – Sources of Pollution
Ch 18 – Effects of Pollution
Ch 19 – Preventive Measures
Ch 20 – Natural Regions of the World
Find the Odd Man Out
- Air, Glass, Water, Mirror
Answer: Mirror
Explanation: Mirror reflects light, others allow refraction. - Refraction, Reflection, Lateral shift, Dispersion
Answer: Reflection
Explanation: Others involve bending or deviation due to medium change. - Vacuum, Water, Glass, Diamond
Answer: Vacuum
Explanation: Vacuum does not cause refraction; others are optical media. - Normal, Incident ray, Refracted ray, Emergent ray
Answer: Normal
Explanation: Normal is a reference line, others are light rays. - Angle of incidence, Angle of refraction, Angle of deviation, Critical angle
Answer: Angle of deviation
Explanation: Others are formed at a single boundary; deviation involves prism path. - Prism, Glass block, Plane mirror, Glass slab
Answer: Plane mirror
Explanation: Plane mirror only reflects, others refract. - Water, Glass, Optical fibre, Mirror
Answer: Mirror
Explanation: Mirror does not allow refraction or Total Internal Reflection. - Sin i, Sin r, μ, Speed
Answer: Speed
Explanation: Others are part of Snell’s law formula. - Lateral shift, Apparent depth, Twinkling, Total Internal Reflection
Answer: Total Internal Reflection
Explanation: Total Internal Reflection involves complete reflection, others are due to partial refraction. - Mirage, Prism, Periscope, Optical fibre
Answer: Prism
Explanation: Others use Total Internal Reflection; prism shows deviation and dispersion. - Refraction, TIR, Absorption, Dispersion
Answer: Absorption
Explanation: Others involve light travel or bending; absorption is energy loss. - Glass, Water, Diamond, Aluminium
Answer: Aluminium
Explanation: Aluminium is opaque; others are transparent media. - Optical density, Medium, Speed of light, Magnetic field
Answer: Magnetic field
Explanation: Magnetic field doesn’t affect refraction directly. - Vacuum, Transparent, Denser, Opaque
Answer: Opaque
Explanation: Opaque doesn’t allow light transmission. - i > C, μ = 1, TIR, Dense to rare
Answer: μ = 1
Explanation: Refractive index of 1 means no refraction occurs. - 30°, 45°, 60°, 90°
Answer: 90°
Explanation: 90° means light grazes the surface; others are incident angles. - Normal incidence, Critical angle, Total Internal Reflection, Minimum deviation
Answer: Minimum deviation
Explanation: It relates to prisms, not boundary refraction. - Real depth, Apparent depth, Image distance, Critical angle
Answer: Critical angle
Explanation: Others relate to depth perception. - Refracted ray, Incident ray, Reflected ray, Normal
Answer: Normal
Explanation: Normal is not a light ray. - μ = sin i / sin r, μ = c/v, v = fλ, F = ma
Answer: F = ma
Explanation: It’s Newton’s law, not optics-related. - Diamond, Glass, Water, Wood
Answer: Wood
Explanation: Wood is opaque, others are transparent. - Periscope, Binoculars, Prism, Telescope mirror
Answer: Telescope mirror
Explanation: It reflects without using Total Internal Reflection or prisms. - Prism, Equilateral triangle, Glass block, Triangular prism
Answer: Equilateral triangle
Explanation: It’s a shape, not an optical device. - Twinkling, Total Internal Reflection, Refraction, Bending
Answer: Total Internal Reflection
Explanation: Others involve partial refraction, Total Internal Reflection is full internal reflection. - μglass > μair, μdiamond > μwater, μair > μglass, μwater < μdiamond
Answer: μair > μglass
Explanation: Air always has lower μ than glass. - Optical fibre, Total Internal Reflection, Reflection, μ = 1
Answer: μ = 1
Explanation: Refractive index = 1 means no Total Internal Reflection is possible. - Speed, Frequency, Wavelength, Medium
Answer: Frequency
Explanation: Frequency does not change during refraction. - Apparent depth, Real depth, Lateral shift, Critical angle
Answer: Critical angle
Explanation: Others are displacement-related; critical angle defines Total Internal Reflection. - Glass slab, Thick mirror, Rectangular block, Plane mirror
Answer: Plane mirror
Explanation: It doesn’t produce lateral shift or internal refraction. - Critical angle, Total Internal Reflection, Reflection, Lateral shift
Answer: Lateral shift
Explanation: Not related to TIR or reflection. - Laser, LED, Light ray, Radio wave
Answer: Radio wave
Explanation: Not part of optical visible spectrum. - Pin method, Prism method, Protractor, Newton ring
Answer: Newton ring
Explanation: It’s interference-based, not refraction-related. - Refractive index, Angle of prism, Speed of light, Power of lens
Answer: Power of lens
Explanation: Not discussed in this chapter. - Deviation, Bending, Straight-line motion, Refraction
Answer: Straight-line motion
Explanation: Others involve path change. - Normal, Emergent ray, Reflected ray, Incident ray
Answer: Reflected ray
Explanation: Reflection is not primary in refraction chapter. - μwater = 1.33, μglass = 1.5, μair = 1.00, μvacuum = 1.5
Answer: μvacuum = 1.5
Explanation: Vacuum has μ = 1, not 1.5. - Angle of prism, Angle of deviation, Angle of incidence, Angle of elevation
Answer: Angle of elevation
Explanation: Not related to light or optics. - Ray diagram, Snell’s law, Focal length, Refractive index
Answer: Focal length
Explanation: Belongs to lenses, not refraction through block or prism. - Glass, Water, Air, Black paper
Answer: Black paper
Explanation: It’s opaque, does not allow light transmission. - Right-angle prism, Plane mirror, Optical fibre, Equilateral prism
Answer: Plane mirror
Explanation: It reflects without internal refraction. - μ = 1.5, μ = 1.33, μ = 2.42, μ = 0.5
Answer: μ = 0.5
Explanation: μ is never less than 1 in practice. - Real image, Apparent image, Virtual image, Lateral shift
Answer: Lateral shift
Explanation: It’s a shift, not an image. - Laser, Mirror, Prism, Glass slab
Answer: Laser
Explanation: It’s a light source, others are optical elements. - Mirror, TIR, Prism, Refraction
Answer: Mirror
Explanation: Does not involve medium change or internal path. - Critical angle, i = 0°, sin i / sin r, μ = c / v
Answer: i = 0°
Explanation: No refraction occurs when i = 0°. - Refractive index, Frequency, Angle of prism, Speed of light
Answer: Frequency
Explanation: Frequency remains unchanged. - 42°, 60°, 90°, 180°
Answer: 180°
Explanation: Not a typical angle in refraction studies. - Base, Apex, Height, Normal
Answer: Height
Explanation: Not a parameter used in prism ray diagrams. - Periscope, Microscope, Binoculars, Optical fibre
Answer: Microscope
Explanation: Works mainly with lenses, not Total Internal Reflection. - Air, Vacuum, Water, Mercury
Answer: Mercury
Explanation: It’s opaque and reflective; others are transparent.
Match the Pair
Set 1 – Match the Pairs
Column A
- Refraction
- Refractive index
- Normal incidence
- Speed of light in glass
- Angle of incidence
Column B
a) Light passes undeviated
b) Between incident ray and normal
c) 2 × 10⁸ m/s
d) Bending of light
e) Ratio of speed of light in vacuum to speed in medium
Correct Answers – Set 1
1 – d
2 – e
3 – a
4 – c
5 – b
Set 2 – Match the Pairs
Column A
- Glass slab
- Lateral shift
- Denser to rarer
- Speed of light in vacuum
- Critical angle
Column B
a) Refracted ray at 90°
b) 3 × 10⁸ m/s
c) Emergent ray is parallel to incident ray
d) Displacement of emergent ray
e) Light bends away from normal
Correct Answers – Set 2
1 – c
2 – d
3 – e
4 – b
5 – a
Set 3 – Match the Pairs
Column A
- Total Internal Reflection
- Optical fibre
- Mirage
- Right-angle prism
- Periscope
Column B
a) Used in endoscopy
b) Complete reflection within denser medium
c) Produces 90° or 180° deviation
d) Uses two reflecting prisms
e) Optical illusion due to hot air layers
Correct Answers – Set 3
1 – b
2 – a
3 – e
4 – c
5 – d
Set 4 – Match the Pairs
Column A
- Twinkling of stars
- Apparent depth
- Real depth
- Refraction through prism
- Refracted ray
Column B
a) Greater than apparent depth
b) Due to atmospheric refraction
c) Enters second medium
d) Appears shallower
e) Deviates towards base
Correct Answers – Set 4
1 – b
2 – d
3 – a
4 – e
5 – c
Set 5 – Match the Pairs
Column A
- μ = c / v
- μ = sin i / sin r
- Lateral shift increases with
- Critical angle formula
- Frequency during refraction
Column B
a) Remains unchanged
b) sin C = 1 / μ
c) Thickness of glass slab
d) Speed-based definition
e) Snell’s Law
Correct Answers – Set 5
1 – d
2 – e
3 – c
4 – b
5 – a
Set 6 – Match the Pairs
Column A
- Light in vacuum
- Light in water
- Light in diamond
- Light in air
- Speed reduces when
Column B
a) Enters denser medium
b) 3 × 10⁸ m/s
c) 2.25 × 10⁸ m/s
d) Refractive index ≈ 1
e) Highest optical density
Correct Answers – Set 6
1 – b
2 – c
3 – e
4 – d
5 – a
Set 7 – Match the Pairs
Column A
- Incident ray
- Normal
- Emergent ray
- Plane mirror
- Total Internal Reflection prism
Column B
a) Reference for angle measurement
b) Exits after second refraction
c) Reflects light without refraction
d) Enters medium at an angle
e) Reflects completely inside prism
Correct Answers – Set 7
1 – d
2 – a
3 – b
4 – c
5 – e
Set 8 – Match the Pairs
Column A
- Apex of prism
- Base of prism
- Deviation
- Dispersion
- White light
Column B
a) Combination of 7 colours
b) Bottom face of prism
c) Change in direction of light
d) Narrow tip of prism
e) Splitting into colours
Correct Answers – Set 8
1 – d
2 – b
3 – c
4 – e
5 – a
Set 9 – Match the Pairs
Column A
- Refracted ray
- Total Internal Reflection
- Critical angle
- Rarer to denser
- Equilateral prism
Column B
a) All angles 60°
b) Light bends towards normal
c) Angle of incidence for 90° refraction
d) No light escapes into second medium
e) Travels in second medium
Correct Answers – Set 9
1 – e
2 – d
3 – c
4 – b
5 – a
Set 10 – Match the Pairs
Column A
- Apparent bending of stick
- Mirror reflection
- Total Internal Reflection in prism
- Minimum deviation
- Twinkling of stars
Column B
a) Occurs due to equal angles of incidence and emergence
b) Caused by atmospheric refraction
c) Used in binoculars and periscopes
d) Due to refraction at water surface
e) Occurs on reflecting surfaces only
Correct Answers – Set 10
1 – d
2 – e
3 – c
4 – a
5 – b
Short Answer Questions
- What is refraction of light?
Refraction is the bending of light as it passes from one transparent medium to another. - Why does light refract?
Light refracts because its speed changes in different media. - What is the speed of light in vacuum?
The speed of light in vacuum is 3 × 10⁸ m/s. - What is the formula for refractive index using speed?
Refractive index μ = c / v. - What is the formula for refractive index using angles?
Refractive index μ = sin i / sin r. - What is meant by optical density?
Optical density refers to the ability of a medium to slow down light. - Define normal incidence.
Normal incidence occurs when a light ray strikes the boundary at 90°. - What happens to a ray at normal incidence?
The ray passes undeviated. - Define critical angle.
The critical angle is the angle of incidence in the denser medium for which the angle of refraction in the rarer medium is 90°. - What is the condition for Total Internal Reflection?
Total Internal Reflection occurs when the angle of incidence exceeds the critical angle and light travels from a denser to a rarer medium. - Which type of medium has a higher refractive index: water or glass?
Glass has a higher refractive index than water. - What is the refractive index of air approximately?
The refractive index of air is approximately 1. - What does the emergent ray in a glass slab look like?
It is parallel to the incident ray but laterally displaced. - What is lateral shift?
Lateral shift is the perpendicular distance between the incident and emergent ray in a glass slab. - Name a use of Total Internal Reflection.
Total Internal Reflection is used in optical fibres. - Why does a coin in water appear raised?
Due to refraction, the coin appears raised because apparent depth is less than real depth. - What is the unit of refractive index?
Refractive index has no unit. - What happens to the speed of light when it enters a denser medium?
The speed of light decreases. - What is meant by the term μ?
μ is the refractive index of a medium. - What causes twinkling of stars?
Twinkling is caused by atmospheric refraction. - What is a mirage?
A mirage is an optical illusion caused by Total Internal Reflection in layers of hot air. - What is meant by the principle of reversibility of light?
It states that the path of light is reversible. - What happens when light passes from rarer to denser medium?
It bends towards the normal. - What happens when light passes from denser to rarer medium?
It bends away from the normal. - What type of image does a right-angle prism form?
It forms an erect and laterally inverted image. - What is meant by dispersion of light?
It is the splitting of white light into its constituent colours. - What is the critical angle for water to air?
The critical angle for water to air is approximately 48.6°. - Name the type of reflection in prisms used in periscopes.
Total Internal Reflection. - State one condition for Total Internal Reflection.
Light must travel from denser to rarer medium. - What type of deviation does a right-angle prism give?
It gives 90° or 180° deviation. - What remains constant when light refracts?
Frequency remains constant. - What property of light changes during refraction?
Its speed and wavelength change. - Name the component that causes deviation in a prism.
The refracting surfaces cause deviation. - What is meant by real depth?
It is the actual depth of an object under a transparent medium. - What is apparent depth?
It is the depth at which an object appears due to refraction. - What is the relationship between real and apparent depth?
Apparent depth = Real depth ÷ μ. - Why is the sky blue?
Due to scattering, not refraction. - What causes the shift in the position of stars?
Atmospheric refraction causes it. - What is the role of refractive index in refraction?
It determines how much light bends. - What is the deviation produced by a prism dependent on?
On the angle of incidence and refractive index. - What is the minimum deviation in a prism?
It is the smallest angle between incident and emergent rays. - Name one optical instrument that uses Total Internal Reflection.
Binoculars use Total Internal Reflection. - What does the emergent ray do in a rectangular slab?
It emerges parallel to the incident ray. - Which color deviates the most in dispersion?
Violet deviates the most. - Which color deviates the least in dispersion?
Red deviates the least. - What is the unit of angle of incidence?
Degrees (°). - Define angle of refraction.
It is the angle between the refracted ray and the normal. - In which medium does light travel slowest: air, water, or glass?
Light travels slowest in glass. - In a prism, does the emergent ray deviate towards the base or the apex?
It deviates towards the base. - Is Total Internal Reflection possible in vacuum?
No, it is not possible in vacuum.
Puzzles
Puzzle 1:
A fish in a pond sees a fly just above the water surface. The fish jumps to catch the fly, but misses. Why?
Answer: Due to refraction, the position of the fly appears closer than it actually is.
Puzzle 2:
A light ray enters a glass block from air and emerges parallel to the incident ray. What phenomenon explains this?
Answer: Refraction with lateral displacement in a rectangular block.
Puzzle 3:
You shine a laser through a rectangular glass slab. The beam exits displaced but parallel. How could this be used in alignment technology?
Answer: To fine-tune instruments while preserving direction but accounting for shift.
Puzzle 4:
A person places a coin in a bowl and slowly pours water into it. The coin becomes visible without moving. Explain.
Answer: Refraction makes the coin appear at a higher position than its actual depth.
Puzzle 5:
A student aims a laser at a glass slab. At what angle must they hit to avoid deviation?
Answer: At 90°, the ray passes undeviated.
Puzzle 6:
Why does a pool appear shallower than it actually is?
Answer: Apparent depth is less due to refraction.
Puzzle 7:
If the speed of light in air is 3 × 10⁸ m/s and in glass is 2 × 10⁸ m/s, what is the refractive index of glass?
Answer: μ = 3/2 = 1.5
Puzzle 8:
You use a glass prism with angles 60°, 60°, 60°. Will light bend toward or away from the base?
Answer: Toward the base, due to refraction.
Puzzle 9:
If a prism deviates light by 90°, which optical device could be designed using this?
Answer: A periscope using a right-angle prism.
Puzzle 10:
A prism causes deviation of 180°. Which optical function is being performed?
Answer: Inversion using Total Internal Reflection.
Puzzle 11:
A person sees a mirage in the desert. What’s the scientific explanation?
Answer: Total Internal Reflection due to temperature gradient in air.
Puzzle 12:
Light enters a water droplet and exits as a rainbow. What sequence of events occurred?
Answer: Refraction → Internal reflection → Refraction
Puzzle 13:
Why does a diamond sparkle more than glass?
Answer: Higher refractive index and lower critical angle causing multiple Total Internal Reflections.
Puzzle 14:
Light is incident from glass to air at an angle of 80°. Will refraction or reflection occur?
Answer: Total Internal Reflection if angle > critical angle.
Puzzle 15:
Why can you see your image using a prism but not a plane mirror underwater?
Answer: Prism uses Total Internal Reflection with less light loss than mirror underwater.
Puzzle 16:
An erect image is formed using a right-angle prism. What is the deviation angle?
Answer: Deviation = 180°
Puzzle 17:
Why are optical fibers unaffected by bending?
Answer: Light is trapped via repeated Total Internal Reflection.
Puzzle 18:
A stick appears bent in water. What causes this illusion?
Answer: Refraction at air-water interface.
Puzzle 19:
Light incident on a glass slab travels undeviated. What can be inferred about the incidence angle?
Answer: It is normal incidence (90°).
Puzzle 20:
Twinkling of stars is due to?
Answer: Refraction by atmospheric layers.
Puzzle 21:
Why can’t you see through a glass prism if light is incident at too large an angle?
Answer: Because it undergoes Total Internal Reflection and doesn’t emerge from the other side.
Puzzle 22:
You are designing a prism-based periscope. What must be true about the critical angle for successful reflection?
Answer: The angle of incidence must be greater than the critical angle of the prism material.
Puzzle 23:
Why are prisms preferred over mirrors in binoculars?
Answer: Prisms reflect light more efficiently using Total Internal Reflection and don’t degrade like mirrors.
Puzzle 24:
Why doesn’t light refract when entering from vacuum to air?
Answer: Because the refractive index difference is negligible (both ~1), so no bending occurs.
Puzzle 25:
If a light ray enters from air into a medium and bends away from the normal, what does this indicate?
Answer: It indicates the second medium is optically rarer than air, which is highly unlikely.
Puzzle 26:
Why does a beam of white light split into colours through a prism but not through a glass slab?
Answer: In a prism, angled surfaces cause angular separation; in a slab, dispersion is cancelled by the second refraction.
Puzzle 27:
An underwater diver sees objects above water distorted. Why?
Answer: Due to refraction at the water-air interface altering the apparent position of the object.
Puzzle 28:
Why is the emergent ray parallel to the incident ray in a glass slab experiment?
Answer: Because the two refractions cancel angular deviation, leaving a lateral shift only.
Puzzle 29:
If a laser beam is totally internally reflected inside a prism, what can be said about the incident angle?
Answer: It is greater than the critical angle for that medium-air interface.
Puzzle 30:
Why is frequency unchanged during refraction, though wavelength and speed change?
Answer: Frequency is a property of the source and remains constant across media.
Puzzle 31:
A monochromatic ray is incident at an angle and passes through two prisms. Why doesn’t it split?
Answer: It is monochromatic (single wavelength), so there is no dispersion.
Puzzle 32:
Why do wet roads sometimes appear shiny or mirror-like?
Answer: Because a thin film of water can cause Total Internal Reflection of sky light.
Puzzle 33:
Why does refraction not occur inside a perfectly transparent vacuum tube?
Answer: Refraction needs a boundary between two different media, which doesn’t exist in a vacuum.
Puzzle 34:
Why does the critical angle vary between water and diamond?
Answer: Because critical angle depends on refractive index, and diamond has a much higher index than water.
Puzzle 35:
Why is red light used in fog lights, not violet?
Answer: Red light bends less and scatters less, ensuring better visibility in fog.
Puzzle 36:
If refractive index = 2, what is the critical angle approximately?
Answer: sin C = 1/2 → C ≈ 30°.
Puzzle 37:
A beam of light enters a medium and speeds up. What happens to the angle of refraction?
Answer: It becomes larger than the angle of incidence.
Puzzle 38:
You measure the angle of incidence as 50°, and angle of refraction as 30°. What does this say about the medium?
Answer: The second medium is optically denser (since it bends the ray towards the normal).
Puzzle 39:
Why is lateral shift directly proportional to slab thickness?
Answer: A thicker slab gives light more distance to travel within, increasing shift.
Puzzle 40:
Why is a diamond cut with specific angles?
Answer: To ensure light inside reflects multiple times via Total Internal Reflection, increasing brilliance.
Puzzle 41:
Why does an oil droplet on water show colourful patterns?
Answer: Due to interference and refraction in varying thickness of the droplet layer.
Puzzle 42:
A laser beam travels in glass and emerges into air. If no bending occurs, what can be said?
Answer: The beam was incident normally (perpendicular to the surface).
Puzzle 43:
What happens to wavelength of light as it enters a denser medium?
Answer: It decreases while frequency remains constant.
Puzzle 44:
Why are fish able to see objects above the water in a circular patch?
Answer: This is due to refraction limiting their view to a cone of vision known as Snell’s window.
Puzzle 45:
Why does a glass rod disappear in a liquid of same refractive index?
Answer: No refraction or reflection occurs at the boundary, making the rod invisible.
Puzzle 46:
A laser enters a plastic rod and bends. What is the bending direction if plastic is denser than air?
Answer: It bends towards the normal.
Puzzle 47:
A ray exits a prism at the same angle as it entered but in opposite direction. What deviation has occurred?
Answer: A deviation of 180°.
Puzzle 48:
Why do raindrops sometimes cause double rainbows?
Answer: Due to two successive internal reflections and dispersion in water droplets.
Puzzle 49:
Why are swimming pool tiles hard to judge in depth?
Answer: Refraction makes them appear raised, misleading depth perception.
Puzzle 50:
Why does a light beam curve near a black hole, though it’s a vacuum?
Answer: That is due to gravity (general relativity), not refraction.
Difference Between:
- Difference between Reflection and Refraction
Answer:
- Reflection is the bouncing back of light from a surface.
- Refraction is the bending of light as it passes from one medium to another.
- Difference between Real Depth and Apparent Depth
Answer:
- Real depth is the actual vertical distance of an object below a surface.
- Apparent depth is the perceived depth due to refraction, and it is always less than the real depth.
- Difference between Refracted Ray and Emergent Ray
Answer:
- Refracted ray is the ray that bends when entering a new medium.
- Emergent ray is the ray that comes out of the second surface after passing through a medium.
- Difference between Critical Angle and Angle of Incidence
Answer:
- Critical angle is the angle of incidence in the denser medium for which the angle of refraction becomes 90°.
- Angle of incidence is the angle between the incident ray and the normal.
- Difference between Normal Incidence and Oblique Incidence
Answer:
- In normal incidence, light strikes perpendicular to the surface (angle of incidence = 0°).
- In oblique incidence, light strikes at any angle other than 0°.
- Difference between Total Internal Reflection and Refraction
Answer:
- Total Internal Reflection occurs when the light is completely reflected back into the denser medium.
- Refraction occurs when part of the light passes into the rarer medium and bends.
- Difference between Rarer Medium and Denser Medium
Answer:
- A rarer medium allows light to travel faster and has a lower refractive index.
- A denser medium slows down light and has a higher refractive index.
- Difference between Speed of Light in Air and in Glass
Answer:
- Speed of light in air is approximately 3 × 10⁸ m/s.
- Speed of light in glass is about 2 × 10⁸ m/s, which is slower due to higher optical density.
- Difference between Glass Slab and Glass Prism
Answer:
- A glass slab has parallel sides and produces no angular deviation but only lateral shift.
- A glass prism has non-parallel sides and deviates the light beam angularly.
- Difference between Dispersion and Refraction
Answer:
- Dispersion is the splitting of white light into its component colours.
- Refraction is the bending of light when it travels from one medium to another.
- Difference between Optical Density and Mass Density
Answer:
- Optical density refers to how much a medium slows down light.
- Mass density is the mass per unit volume of a substance.
- Difference between Total Internal Reflection and Regular Reflection
Answer:
- Total Internal Reflection occurs only at the boundary of a denser to rarer medium when angle > critical angle.
- Regular reflection occurs on a polished surface and does not depend on media or critical angle.
- Difference between Angle of Refraction and Angle of Deviation
Answer:
- Angle of refraction is the angle between refracted ray and normal.
- Angle of deviation is the angle between the direction of incident ray and emergent ray.
- Difference between Real Image and Apparent Image due to Refraction
Answer:
- Real image is formed where light rays actually meet.
- Apparent image due to refraction is a virtual image seen due to bending of light rays.
- Difference between Mirror and Prism in terms of reflection
Answer:
- A mirror reflects light by surface reflection, and some energy is lost.
- A prism reflects light using Total Internal Reflection, conserving more light energy.
- Difference between Refraction in a Prism and in a Glass Slab
Answer:
- In a prism, the emergent ray is deviated at an angle to the incident ray.
- In a glass slab, the emergent ray is parallel to the incident ray with lateral shift.
- Difference between Refractive Index and Critical Angle
Answer:
- Refractive index is the ratio of speed of light in vacuum to that in a medium.
- Critical angle is the angle of incidence in the denser medium at which angle of refraction is 90°.
- Difference between Convex Lens and Prism
Answer:
- A convex lens bends rays toward a focal point and forms images.
- A prism deviates and disperses light without focusing it.
- Difference between Reflection in Plane Mirror and Refraction in Glass Slab
Answer:
- Reflection in a mirror causes a reversed image without changing medium.
- Refraction in glass slab causes displacement and apparent shift of the object.
- Difference between Bending Towards and Away from Normal
Answer:
- Light bends towards the normal when it enters a denser medium.
- Light bends away from the normal when it enters a rarer medium.
Assertion and Reason
Key to options:
A. Both Assertion and Reason are true, and Reason is the correct explanation.
B. Both Assertion and Reason are true, but Reason is not the correct explanation.
C. Assertion is true, but Reason is false.
D. Assertion is false, but Reason is true.
- Assertion: Light bends towards the normal when entering a denser medium.
Reason: The speed of light increases in denser medium.
Answer: C
Explanation: Light slows down in denser medium. - Assertion: Light undergoes deviation when passing through a prism.
Reason: A prism has unequal refracting surfaces causing refraction.
Answer: A
Explanation: Both are true and directly related. - Assertion: At normal incidence, refraction does not occur.
Reason: Light passes undeviated along the normal.
Answer: A
Explanation: Both are true and related. - Assertion: The critical angle for glass is greater than that of water.
Reason: Glass has higher refractive index than water.
Answer: C
Explanation: Critical angle is smaller for higher refractive index. - Assertion: Total Internal Reflection occurs only from rarer to denser medium.
Reason: In rarer medium light travels faster.
Answer: D
Explanation: Total Internal Reflection occurs from denser to rarer. - Assertion: Lateral shift increases with thickness of the glass slab.
Reason: More thickness means greater deviation from parallel emergence.
Answer: A - Assertion: Refraction causes change in frequency of light.
Reason: The wavelength of light changes when passing between media.
Answer: C
Explanation: Frequency remains unchanged. - Assertion: Apparent depth is less than real depth.
Reason: Light bends away from normal when coming from water to air.
Answer: A - Assertion: In Total Internal Reflection, the refracted ray disappears.
Reason: Light is completely reflected inside the denser medium.
Answer: A - Assertion: Critical angle depends on the pair of media.
Reason: Refractive index is different for different materials.
Answer: A - Assertion: The speed of light is constant in all media.
Reason: Light always travels at m/s.
Answer: D - Assertion: Light cannot undergo Total Internal Reflection from water to glass.
Reason: Total Internal Reflection requires light to move from denser to rarer medium.
Answer: A - Assertion: Angle of deviation in a prism is maximum at minimum deviation position.
Reason: Minimum deviation occurs when angle of incidence equals angle of emergence.
Answer: C - Assertion: Light shows lateral shift while passing through a glass block.
Reason: Lateral shift depends on angle of incidence and thickness.
Answer: A - Assertion: A plane mirror always reflects light by Total Internal Reflection.
Reason: Plane mirror is a reflecting surface.
Answer: D - Assertion: Total Internal Reflection gives brighter images than mirrors.
Reason: There is no loss of light energy in Total Internal Reflection.
Answer: A - Assertion: All transparent materials allow Total Internal Reflection.
Reason: All materials have a critical angle.
Answer: C - Assertion: Refraction does not occur when the light travels from vacuum to glass.
Reason: Vacuum has no particles.
Answer: D - Assertion: A prism can produce both deviation and dispersion.
Reason: The refractive index is same for all wavelengths.
Answer: C - Assertion: Total Internal Reflection is used in optical fibres.
Reason: It helps transmit light with minimal loss.
Answer: A - Assertion: Refraction changes the path of light.
Reason: Change in speed causes bending of light at interface.
Answer: A - Assertion: Refractive index of vacuum is 0.
Reason: Light travels infinitely fast in vacuum.
Answer: D - Assertion: Right-angle prism is used to produce Total Internal Reflection.
Reason: It reflects light without using a mirror.
Answer: A - Assertion: Total Internal Reflection occurs in both directions at boundary.
Reason: Light is fully reflected regardless of direction.
Answer: D - Assertion: A periscope uses plane mirrors only.
Reason: Plane mirrors are preferred over Total Internal Reflection.
Answer: C - Assertion: Apparent depth is seen due to refraction.
Reason: Light bends while coming from denser to rarer medium.
Answer: A - Assertion: Critical angle increases with increase in refractive index.
Reason: Higher refractive index means light bends more.
Answer: C - Assertion: Total Internal Reflection can only happen when incidence angle < critical angle.
Reason: Greater angles prevent reflection.
Answer: D - Assertion: Mirage is a result of Total Internal Reflection.
Reason: Hot air near the ground causes refractive index variation.
Answer: A - Assertion: Twinkling of stars is caused by Total Internal Reflection.
Reason: Light bends due to different layers of atmosphere.
Answer: C - Assertion: A glass prism deviates light towards its base.
Reason: Light slows down inside the prism.
Answer: A - Assertion: Light ray bends away from normal in water to air transition.
Reason: Speed of light increases in air.
Answer: A - Assertion: In Total Internal Reflection, angle of refraction is 90°.
Reason: That defines the critical angle condition.
Answer: B - Assertion: Speed of light is same in all transparent materials.
Reason: Light is a constant-speed wave.
Answer: D - Assertion: Critical angle is smaller for diamond than for water.
Reason: Diamond has higher refractive index.
Answer: A - Assertion: Refractive index = 1 indicates denser medium.
Reason: It shows that light is slowed down.
Answer: D - Assertion: Total Internal Reflection requires incidence in rarer medium.
Reason: Light reflects better in rarer media.
Answer: D - Assertion: Light emerges parallel in a glass block.
Reason: Glass block has parallel sides.
Answer: A - Assertion: Frequency of light remains constant during refraction.
Reason: Only speed and wavelength change.
Answer: A - Assertion: The emergent ray in a prism is undeviated.
Reason: A prism has unequal angles.
Answer: D - Assertion: Total Internal Reflection is more efficient than mirror reflection.
Reason: Total Internal Reflection has zero energy loss.
Answer: A - Assertion: Total Internal Reflection occurs at all angles.
Reason: Light reflects from all surfaces.
Answer: D - Assertion: μ = sin i / sin r is valid for perpendicular incidence.
Reason: At perpendicular incidence, i = 0.
Answer: D - Assertion: Total Internal Reflection can be used to rotate light path.
Reason: It bends light sharply inside prism.
Answer: A - Assertion: Periscopes with prisms are brighter than those with mirrors.
Reason: Total Internal Reflection is more efficient than mirror reflection.
Answer: A - Assertion: Prism shows deviation but not Total Internal Reflection.
Reason: Prisms always transmit light only.
Answer: D - Assertion: Light can bend at 180° in a right-angle prism.
Reason: It reflects completely inside the prism.
Answer: A - Assertion: Lateral shift happens in a plane mirror.
Reason: Mirror has parallel reflecting surfaces.
Answer: D - Assertion: Total Internal Reflection happens if μ is less than 1.
Reason: Light escapes from denser to rarer medium.
Answer: C - Assertion: Critical angle exists only when μ > 1.
Reason: Only then can light move from denser to rarer medium.
Answer: A
True or False
- Refraction is the bending of light when it passes from one medium to another.
Answer: True - Light travels faster in glass than in air.
Answer: False - The speed of light in vacuum is 3 × 10⁸ m/s.
Answer: True - The refractive index of a medium is always less than 1.
Answer: False - Light bends away from the normal when it travels from water to air.
Answer: True - The refractive index has no unit.
Answer: True - The emergent ray from a glass slab is always perpendicular to the incident ray.
Answer: False - A plane mirror produces Total Internal Reflection.
Answer: False - In normal incidence, the light ray passes undeviated.
Answer: True - Total Internal Reflection occurs only when light travels from rarer to denser medium.
Answer: False - A critical angle is defined as the angle of incidence for which the angle of refraction is 90°.
Answer: True - The principle of reversibility applies only to reflection.
Answer: False - Refraction occurs because light changes speed in different media.
Answer: True - The refractive index μ = c/v, where c is the speed of light in vacuum.
Answer: True - Frequency of light changes during refraction.
Answer: False - The apparent depth is less than the real depth.
Answer: True - A prism deviates light away from its base.
Answer: False - The lateral shift in a glass slab depends on its thickness and angle of incidence.
Answer: True - In Total Internal Reflection, light passes into the second medium.
Answer: False - Mirage is caused by Total Internal Reflection in hot air layers.
Answer: True - The angle of incidence must be greater than the critical angle for Total Internal Reflection to occur.
Answer: True - Twinkling of stars is due to atmospheric refraction.
Answer: True - A glass prism can be used to reflect light using Total Internal Reflection.
Answer: True - Total Internal Reflection only occurs at 0° incidence.
Answer: False - A right-angle prism can deviate light by 90° or 180°.
Answer: True - In a glass slab, the incident and emergent rays are parallel.
Answer: True - The formula μ = sin i / sin r is known as Snell’s Law.
Answer: True - Light always bends towards the normal when it travels from any medium to any other medium.
Answer: False - The refractive index of water is less than that of glass.
Answer: True - When light travels from a denser to a rarer medium, it always reflects.
Answer: False - Total Internal Reflection occurs when the angle of incidence is equal to the critical angle.
Answer: False - Critical angle is defined only when light goes from a denser to a rarer medium.
Answer: True - A thick mirror can produce multiple images due to internal reflection.
Answer: True - Dispersion of light is a result of Total Internal Reflection.
Answer: False - An optical fibre uses Total Internal Reflection to transmit signals.
Answer: True - Light changes direction at the boundary due to difference in densities of media.
Answer: True - Angle of deviation in a prism increases uniformly with angle of incidence.
Answer: False - Refracted rays lie on the same side of the normal as incident rays.
Answer: False - Light in diamond travels faster than in water.
Answer: False - Refraction can occur in opaque materials.
Answer: False - The unit of the refractive index is meter per second (m/s).
Answer: False - A 60°-60°-60° prism is called an equilateral prism.
Answer: True - Refractive index is a measure of optical density.
Answer: True - The phenomenon of light bending is not reversible.
Answer: False - Light undergoes refraction at both entry and exit faces of a prism.
Answer: True - In a glass slab, light does not refract at all.
Answer: False - Total Internal Reflection gives brighter images than mirrors.
Answer: True - Refractive index of air is taken approximately as 1.
Answer: True - Refraction cannot occur at oblique incidence.
Answer: False - Real depth is more than apparent depth.
Answer: True
Long Answer Questions
- Define refraction of light and explain why it occurs.
Answer: Refraction of light is the bending of a light ray when it passes from one medium to another of different optical density. It occurs due to a change in the speed of light in different media—faster in rarer medium and slower in denser medium.
- State and explain the laws of refraction of light.
Answer:
First Law: The incident ray, the refracted ray, and the normal to the interface all lie in the same plane.
Second Law (Snell’s Law): The ratio of the sine of the angle of incidence (i) to the sine of the angle of refraction (r) is a constant, i.e.,
sin i / sin r = constant = refractive index (μ).
- Define refractive index and give its two formulas.
Answer: Refractive index (μ) of a medium is the ratio of the speed of light in vacuum (c) to the speed of light in the medium (v).
μ = c / v
It is also given by Snell’s Law: μ = sin i / sin r
- What is meant by optical density? How does it differ from mass density?
Answer: Optical density refers to the ability of a medium to slow down light. A medium with high optical density reduces the speed of light more. It is unrelated to mass density, which is mass per unit volume.
- State the principle of reversibility of light with a diagram.
Answer: The principle states that the path of light is reversible. If light travels from medium A to B, then it would retrace the same path if it travels back from B to A.
- Describe an experiment to verify the laws of refraction using a glass slab.
Answer:
- Place a glass slab on a paper.
- Insert two pins to represent the incident ray and mark them.
- Observe the emergent ray and insert two more pins.
- Draw the incident ray, emergent ray, normal, and refracted ray.
- Measure ∠i and ∠r, and verify that sin i / sin r = constant.
- Define lateral shift. Why does it occur?
Answer: Lateral shift is the perpendicular distance between the incident ray and emergent ray when light passes through a rectangular glass slab. It occurs due to refraction at both surfaces of the slab.
- Explain what is meant by critical angle. Derive the relation between critical angle and refractive index.
Answer: The critical angle is the angle of incidence in the denser medium for which the angle of refraction in the rarer medium is 90°.
sin C = 1 / μ
- Define and explain the phenomenon of Total Internal Reflection.
Answer: Total Internal Reflection is the complete reflection of light back into a denser medium when the angle of incidence exceeds the critical angle. It occurs when light travels from denser to rarer medium.
- List the conditions required for Total Internal Reflection to occur.
Answer:
- Light must travel from a denser to a rarer medium.
- Angle of incidence must be greater than the critical angle.
- Describe the working and application of Total Internal Reflection in optical fibres.
Answer: Optical fibres transmit light by repeated Total Internal Reflection inside a flexible fibre made of glass or plastic. They are used in communication and endoscopy.
- How is Total Internal Reflection used in periscopes and binoculars?
Answer: Right-angle prisms are used to deviate light by 90° or 180° using Total Internal Reflection, which results in brighter images compared to plane mirrors.
- Explain with a diagram the deviation of light through a triangular glass prism.
Answer: In a triangular prism, the incident ray bends towards the base inside the prism due to refraction, and again refracts at the second face. The emergent ray deviates from the original path, and the angle between the incident and emergent rays is the angle of deviation.
- What is angle of deviation? On what factors does it depend?
Answer: It is the angle between the direction of the incident ray and the emergent ray. It depends on the angle of incidence, refractive index, and angle of the prism.
- Explain real and apparent depth with formula.
Answer:
Real depth: Actual depth of an object in a denser medium.
Apparent depth: Depth at which the object appears due to refraction.
Apparent depth = Real depth / μ
- Why does a pencil appear bent in water?
Answer: Due to refraction, the light from the submerged part bends away from the normal when it enters air. This causes the pencil to appear bent.
- Describe the change in speed, wavelength, and frequency of light during refraction.
Answer:
Speed and wavelength change when light enters a different medium. Frequency remains constant.
- What is the significance of refractive index in the design of lenses and prisms?
Answer: Refractive index determines how much light bends, which is crucial in focusing and deviating rays in optical instruments.
- Compare reflection from a plane mirror and Total Internal Reflection in a prism.
Answer:
Plane mirror: Some light is absorbed or transmitted, and images are dimmer.
Total Internal Reflection: Nearly 100% reflection, providing brighter images.
- What is a mirage? Explain its formation.
Answer: A mirage is an optical illusion where light from the sky bends due to refraction in heated air layers, appearing as water on the road. It results from successive Total Internal Reflection.
- How does atmospheric refraction cause the twinkling of stars?
Answer: As starlight passes through Earth’s atmosphere, it refracts through layers of varying densities. These constantly change due to temperature and pressure, making the apparent position of the star shift rapidly, causing the star to twinkle.
- Why does the Sun appear flattened at sunrise and sunset?
Answer: Due to atmospheric refraction, light from the lower edge of the Sun bends more than light from the upper edge. This unequal bending makes the Sun appear flattened horizontally when near the horizon.
- Derive the relation μ = sin i / sin r.
Answer: According to Snell’s law, for light passing from medium 1 to medium 2,
μ = sin i / sin r,
where i is the angle of incidence and r is the angle of refraction. This ratio is constant for a pair of media and defines their relative refractive index.
- Describe how a coin appears raised when placed in water.
Answer: Light from the coin refracts at the water-air boundary and bends away from the normal, making the coin appear at a shallower depth than its real position. This is due to the difference in refractive indices.
- Explain how a right-angle prism is used to deviate light by 90°.
Answer: A right-angle prism has one angle of 90°. When light enters normally on one face, it internally reflects off the hypotenuse at 45°, emerging perpendicular to its original path, thus deviating by 90° using Total Internal Reflection.
- Explain how a right-angle prism deviates light by 180°.
Answer: Light enters perpendicular to one face, undergoes two successive Total Internal Reflections inside the prism, and emerges from the same face it entered but in the opposite direction, resulting in a 180° deviation.
- State two advantages of using prisms instead of mirrors.
Answer:
- Prisms provide brighter images due to Total Internal Reflection (no energy loss).
- Prisms are more durable and offer a better optical surface than coated mirrors.
- Why do stars appear higher than their actual position?
Answer: Atmospheric refraction bends the light from stars towards the normal as it passes through the denser layers near Earth’s surface, shifting the star’s apparent position higher.
- Describe an experiment to measure the refractive index of a glass block.
Answer:
- Place a rectangular glass slab on paper.
- Draw the outline and a normal.
- Mark an incident ray and trace the refracted and emergent rays.
- Measure angles i and r.
- Use μ = sin i / sin r to calculate refractive index.
- What is dispersion? Why does it not occur in a glass slab?
Answer: Dispersion is the splitting of white light into its constituent colors. It does not occur in a glass slab because both parallel surfaces refract light equally, and the angular separation of colors cancels out.
- Describe how apparent depth varies with viewing angle.
Answer: As the viewing angle increases (away from normal), the bending of light increases due to refraction, and the object appears even shallower than its apparent depth at normal viewing.
- What is the importance of the critical angle in Total Internal Reflection?
Answer: The critical angle determines the minimum angle of incidence above which Total Internal Reflection occurs. It is essential for designing optical devices like fibres and prisms.
- What happens when light is incident at an angle less than the critical angle?
Answer: It undergoes partial refraction and partial reflection at the boundary between two media.
- Why is Total Internal Reflection preferred over mirrors in optical devices?
Answer: Total Internal Reflection ensures nearly 100% reflection with no absorption losses, whereas mirrors can lose intensity due to imperfect surfaces or aging of reflective coatings.
- Explain with a diagram why light bends towards the normal in a denser medium.
Answer: As light enters a denser medium, its speed decreases, and the wavefront shortens, causing the ray to bend towards the normal due to the difference in optical density.
- What is the function of cladding in an optical fibre?
Answer: Cladding surrounds the core of the optical fibre and has a lower refractive index. It ensures that light stays within the core through repeated Total Internal Reflection.
- Why do we not observe Total Internal Reflection in daily life often?
Answer: It requires specific conditions—light must travel from a denser to a rarer medium, and the angle of incidence must be greater than the critical angle—which are not common in everyday environments.
- How does light behave at the boundary of two media?
Answer: Depending on the angle of incidence and the refractive indices, light may reflect, refract, or undergo Total Internal Reflection.
- Explain why diamonds sparkle using Total Internal Reflection.
Answer: Due to their high refractive index, diamonds have very small critical angles. Light entering a diamond undergoes multiple Total Internal Reflections, enhancing internal brightness and sparkle.
- How is light affected when entering a prism obliquely?
Answer: It bends towards the base of the prism due to refraction at both surfaces and undergoes deviation. The amount of bending depends on the refractive index and the angle of the prism.
- What is the refractive index of a medium in which light travels at 2 × 10⁸ m/s?
Answer:
μ = c / v = (3 × 10⁸ m/s) / (2 × 10⁸ m/s) = 1.5
- How does temperature affect refractive index?
Answer: Increase in temperature decreases the refractive index of a medium because the medium becomes optically rarer as its density decreases.
- How does pressure affect refraction?
Answer: Increasing pressure increases the optical density of gases, thereby increasing the refractive index.
- What is the purpose of using a glass prism in a spectrometer?
Answer: To disperse white light into its constituent spectral colors for analysis of light sources.
- How is refraction useful in focusing lenses?
Answer: Lenses bend light through refraction to converge or diverge rays, allowing formation of images in optical instruments like cameras and telescopes.
- How does the angle of deviation vary with angle of incidence in a prism?
Answer: The deviation first decreases, reaches a minimum, and then increases as the angle of incidence increases.
- Define minimum deviation in a prism.
Answer: It is the smallest possible deviation produced by a prism when the angle of incidence equals the angle of emergence.
- What are the uses of prisms based on Total Internal Reflection?
Answer:
- Used in periscopes, binoculars, cameras, and surveying instruments
- Provide clear, bright, and erect images through Total Internal Reflection
- What precautions are taken while performing a refraction experiment using a slab?
Answer:
- Ensure normal incidence is correctly drawn
- Use sharp pins for accuracy
- Avoid parallax error while marking rays
- Keep the slab edges aligned properly
- What is the path of a light ray entering a rectangular glass slab obliquely and emerging into air?
Answer:
The ray bends towards the normal while entering the slab, travels straight within the slab, and then bends away from the normal while emerging, resulting in the emergent ray being parallel to the incident ray but laterally shifted.
Give Reasons
- Give reason: A coin in water appears raised.
Answer: Due to refraction of light, the apparent depth of the coin is less than the real depth, making it appear raised.
- Give reason: Light bends when it passes from one medium to another.
Answer: Light bends because its speed changes when moving between media of different optical densities.
- Give reason: No refraction occurs when light hits a boundary normally.
Answer: At normal incidence, the angle between the light and normal is 0°, so the light continues undeviated.
- Give reason: A glass block causes lateral shift.
Answer: Refraction at both surfaces of the glass slab displaces the emergent ray parallel to the incident ray, causing a lateral shift.
- Give reason: A ray bends towards the normal when entering a denser medium.
Answer: In a denser medium, light slows down, so the ray bends towards the normal due to higher optical density.
- Give reason: Refractive index of air is taken as 1.
Answer: Since the speed of light in air is almost the same as in vacuum, its refractive index is nearly 1.
- Give reason: Apparent depth is always less than real depth.
Answer: Light bends away from the normal as it moves from denser to rarer medium, making objects appear shallower.
- Give reason: Total Internal Reflection cannot occur when light travels from rarer to denser medium.
Answer: Total Internal Reflection occurs only when light travels from denser to rarer medium with angle of incidence greater than the critical angle.
- Give reason: Mirrors give less bright images than prisms.
Answer: Mirrors reflect partially, losing some light, while prisms reflect almost all light due to Total Internal Reflection.
- Give reason: Frequency of light does not change during refraction.
Answer: Frequency depends on the source and remains unchanged when light enters a different medium.
- Give reason: Diamonds sparkle more than other stones.
Answer: Diamonds have a high refractive index and very small critical angle, causing multiple Total Internal Reflections.
- Give reason: Glass has a higher refractive index than water.
Answer: Light slows down more in glass than in water, indicating higher optical density and higher refractive index.
- Give reason: Mirage is seen on hot roads.
Answer: Hot air near the road acts as a rarer medium and causes Total Internal Reflection, forming an image of the sky.
- Give reason: Stars appear to twinkle.
Answer: Due to atmospheric refraction, the starlight bends differently through varying air densities, causing its position and brightness to vary.
- Give reason: The Sun appears earlier than actual sunrise.
Answer: Atmospheric refraction bends sunlight before the Sun reaches the horizon, making it visible earlier.
- Give reason: A prism deviates light.
Answer: The angled surfaces of a prism cause the light to refract twice at different angles, resulting in deviation.
- Give reason: Right-angle prisms are used in optical instruments.
Answer: They reflect light efficiently using Total Internal Reflection, providing erect and bright images.
- Give reason: Total Internal Reflection is used in optical fibres.
Answer: It allows light to travel through the fibre without escaping, even around curves, ensuring efficient signal transmission.
- Give reason: Violet light deviates more than red light.
Answer: Violet has a shorter wavelength and slows down more in denser media, resulting in greater bending.
- Give reason: Refraction occurs at the boundary of two transparent media.
Answer: Because light changes speed at the boundary, leading to a change in direction (refraction).
- Give reason: The emergent ray from a glass slab is parallel to the incident ray.
Answer: The second refraction at the opposite face cancels the angular deviation caused at the first face.
- Give reason: The angle of deviation changes with angle of incidence.
Answer: Refraction depends on the angle of incidence, which affects how much light bends inside the prism.
- Give reason: Right-angle prism deviates light by 180°.
Answer: Two Total Internal Reflections within the prism reverse the direction of the incident light ray.
- Give reason: Lateral shift increases with thickness of glass slab.
Answer: A thicker slab provides a longer path within the medium, increasing the parallel displacement.
- Give reason: Light rays from under water bend away from the normal when emerging.
Answer: Light is moving from a denser to a rarer medium, so it speeds up and bends away from the normal.
- Give reason: Refraction does not occur in opaque materials.
Answer: Light cannot pass through opaque materials, hence no change in speed or direction takes place.
- Give reason: Refraction is not observed when both media have same refractive index.
Answer: Since the speed of light remains constant, there is no bending at the boundary.
- Give reason: Light emerges undeviated if the incident ray is normal to a glass slab.
Answer: The ray enters and exits perpendicular to the surfaces, so no angular bending occurs.
- Give reason: In optical fibres, cladding has lower refractive index than core.
Answer: This ensures Total Internal Reflection occurs at the boundary, keeping the light trapped inside the core.
- Give reason: Plane mirrors are not preferred in binoculars.
Answer: They absorb part of the light and can degrade over time, while prisms ensure better reflection using Total Internal Reflection.
- Give reason: The sky appears blue.
Answer: Though not due to refraction, it is due to scattering of shorter (blue) wavelengths by air molecules.
- Give reason: Angle of refraction increases with decreasing refractive index.
Answer: In a rarer medium, light bends more away from the normal, increasing the angle of refraction.
- Give reason: Red light bends the least in a prism.
Answer: Red has the longest wavelength, hence it is refracted the least compared to other colours.
- Give reason: Optical density is not the same as mass density.
Answer: Optical density refers to how a medium slows down light, not its mass per unit volume.
- Give reason: Refractive index is a dimensionless quantity.
Answer: It is the ratio of two speeds (or sines of angles), so it has no unit or dimension.
- Give reason: Light doesn’t bend at vacuum–air boundary.
Answer: Since the refractive index of air is nearly 1, light doesn’t change speed appreciably, so no significant bending occurs.
- Give reason: Total Internal Reflection gives brighter images than metallic reflection.
Answer: Total Internal Reflection results in almost 100% reflection, while metallic surfaces absorb some light.
- Give reason: Light cannot travel through opaque bodies.
Answer: Opaque materials do not allow transmission of light; they either absorb or reflect it.
- Give reason: White light disperses into spectrum through a prism.
Answer: Different colours of light have different speeds in glass, so they refract at different angles.
- Give reason: Refraction causes object in water to appear broken or displaced.
Answer: Light rays from the submerged part bend at the surface, changing their path and creating visual distortion.
- Give reason: Stars seem to shift position constantly.
Answer: Atmospheric refraction varies with air density, continuously bending starlight in different directions.
- Give reason: Speed of light is less in glass than in air.
Answer: Glass has higher optical density than air, so it slows down light more.
- Give reason: Emergent ray in a glass slab is laterally displaced.
Answer: Double refraction at two parallel surfaces results in lateral shift of the light ray.
- Give reason: Light rays undergo dispersion in a prism but not in a slab.
Answer: The angled surfaces of the prism separate colours, while parallel sides of a slab cancel angular separation.
- Give reason: A lens uses refraction for image formation.
Answer: Lenses are made of transparent material with curved surfaces that bend light rays via refraction to form images.
- Give reason: Air bubbles in water shine when viewed from above.
Answer: Light from inside the bubble undergoes Total Internal Reflection at the curved surface.
- Give reason: Rainbows are not formed in glass prisms.
Answer: Rainbows require dispersion of sunlight in water droplets and are not seen from artificial glass refraction.
- Give reason: Total Internal Reflection cannot occur at any angle.
Answer: It only occurs when light travels from denser to rarer medium and the angle of incidence exceeds the critical angle.
- Give reason: Sun appears red at sunrise and sunset.
Answer: Longer path through atmosphere causes scattering of shorter wavelengths, leaving mostly red light.
- Give reason: Refraction is used in spectacle lenses.
Answer: Lenses refract light to correct the path and focus it properly on the retina to correct vision.
Arrange the Words
Case Studies
Case Study 1:
A pencil is partially immersed in a glass of water. The pencil appears bent at the water surface.
Question: What causes this visual distortion?
Answer: Refraction of light at the water-air boundary.
Case Study 2:
A laser beam enters a rectangular glass block at an angle and emerges from the opposite side displaced but parallel.
Question: What is this phenomenon called?
Answer: Lateral shift due to refraction.
Case Study 3:
While diving, Riya sees a stone that appears closer than it is.
Question: Why does the stone appear raised?
Answer: Due to refraction, the apparent depth is less than the real depth.
Case Study 4:
A light ray enters a prism and bends towards the base.
Question: Why does light bend towards the base of the prism?
Answer: Because of refraction through the inclined surfaces of the prism.
Case Study 5:
A coin placed at the bottom of an empty bowl becomes visible when water is added.
Question: Why does the coin become visible without moving?
Answer: Because refraction raises the apparent position of the coin.
Case Study 6:
An optical fibre transmits light signals over long distances.
Question: What principle is used in optical fibres to trap light inside?
Answer: Total Internal Reflection.
Case Study 7:
Twinkling of stars is observed on a clear night.
Question: What causes stars to appear to twinkle?
Answer: Atmospheric refraction due to temperature and density variations in air.
Case Study 8:
A student places a laser beam at 90° incidence on a glass slab.
Question: What will happen to the beam inside the slab?
Answer: It will pass straight without deviation.
Case Study 9:
An observer sees a mirage on a hot road where water seems to appear at a distance.
Question: What phenomenon causes this illusion?
Answer: Total Internal Reflection in air layers of varying temperature.
Case Study 10:
Light passes from glass into air with an angle of incidence of 60° and does not emerge.
Question: What condition is satisfied here?
Answer: Angle of incidence is greater than the critical angle, causing Total Internal Reflection.
Case Study 11:
A periscope uses prisms instead of mirrors.
Question: Why are prisms preferred in optical instruments?
Answer: Prisms reflect almost all light using Total Internal Reflection, giving a brighter image.
Case Study 12:
A prism splits white light into seven colours.
Question: What physical property causes different colours to bend by different amounts?
Answer: Different wavelengths have different refractive indices, causing dispersion.
Case Study 13:
An object underwater looks larger and closer than it is.
Question: What optical phenomenon is responsible?
Answer: Refraction at the water-air interface.
Case Study 14:
A beam of light enters a medium and its speed reduces.
Question: What happens to the path of light?
Answer: It bends towards the normal due to refraction.
Case Study 15:
In an experiment, the angle of incidence is gradually increased until the refracted ray just grazes the surface.
Question: What is the incident angle called at this point?
Answer: Critical angle.
Case Study 16:
In a diamond, most of the incident light reflects internally before emerging.
Question: What optical phenomenon makes diamonds sparkle?
Answer: Multiple Total Internal Reflections due to high refractive index.
Case Study 17:
A student views a ray diagram where the incident and emergent rays are parallel in a glass slab.
Question: What does this suggest about the path inside the slab?
Answer: The ray refracts twice, causing lateral shift but no net angular deviation.
Case Study 18:
A swimmer looks up at a circular patch of light above.
Question: What is this visual region called?
Answer: Snell’s window – due to refraction limiting the angle of visible light from above.
Case Study 19:
A microscope uses a glass lens.
Question: Why does a lens bend light rays?
Answer: Because of refraction due to the curvature and optical density difference.
Case Study 20:
Sunrise is observed 2 minutes before the Sun actually crosses the horizon.
Question: What causes this early appearance?
Answer: Atmospheric refraction bends sunlight, making the Sun appear earlier.
Numericals
- A ray of light travels from air into glass. Speed of light in air = 3 × 10⁸ m/s, in glass = 2 × 10⁸ m/s. Find refractive index of glass.
Solution:
Refractive index (n) = Speed in air / Speed in glass = (3 × 10⁸) / (2 × 10⁸) = 1.5
- Calculate the speed of light in a diamond. Refractive index of diamond = 2.42; speed in air = 3 × 10⁸ m/s.
Solution:
Speed in diamond = Speed in air / Refractive index = (3 × 10⁸) / 2.42 ≈ 1.24 × 10⁸ m/s
- A light ray passes from air (n = 1.00) into water (n = 1.33) with angle of incidence = 30°. Find angle of refraction.
Solution:
Using Snell’s Law: n₁ sin i = n₂ sin r
1.00 × sin(30°) = 1.33 × sin r
0.5 = 1.33 × sin r → sin r = 0.5 / 1.33 ≈ 0.3759
Angle r = sin⁻¹(0.3759) ≈ 22.09°
- Real depth of a pool is 2.5 m. Refractive index of water is 1.33. Calculate the apparent depth.
Solution:
Apparent depth = Real depth / Refractive index = 2.5 / 1.33 ≈ 1.88 m
- A coin appears raised by 4 cm when in water. Refractive index of water = 1.33. Calculate real depth.
Solution:
Real depth = Apparent depth × Refractive index = 4 × 1.33 = 5.32 cm
- A beam travels from glass to air. Critical angle = 42°. What is refractive index of glass?
Solution:
sin C = 1/n → sin 42° = 1/n → 0.6691 = 1/n → n = 1 / 0.6691 = 1.495
- A light ray enters a glass slab at 45° and refracts at 28°. Find refractive index.
Solution:
n = sin i / sin r = sin 45° / sin 28° = 0.7071 / 0.4695 ≈ 1.506
- In a glass prism, angle of prism = 60° and angle of minimum deviation = 38°. Find refractive index.
Solution:
n = sin[(A + D) / 2] / sin(A / 2) = sin(49°) / sin(30°) = 0.7547 / 0.5 = 1.509
- A ray travels from a medium of refractive index 1.5 into air. Calculate critical angle.
Solution:
sin C = 1 / n = 1 / 1.5 = 0.6667 → C = sin⁻¹(0.6667) = 41.8°
- Light passes from air to a medium and bends towards the normal. What can be inferred about the speed in the medium if n = 1.6?
Solution:
Speed in medium = c / n = (3 × 10⁸) / 1.6 = 1.875 × 10⁸ m/s
- A light ray enters a prism with angle of incidence = 40° and emerges at 60°. If angle of prism = 60°, calculate angle of deviation.
Solution:
Angle of deviation = i + e – A = 40° + 60° – 60° = 40°
- Refractive index of water = 1.33. Find the speed of light in water.
Solution:
Speed = 3 × 10⁸ / 1.33 ≈ 2.26 × 10⁸ m/s
- A ray is incident at 90° to a glass slab. What will be the angle of refraction?
Solution:
Normal incidence implies angle = 0°. Thus, angle of refraction = 0°
- Refractive index = 1.5. Find sin of critical angle.
Solution:
sin C = 1/n = 1/1.5 = 0.6667
- Apparent depth = 15 cm. Refractive index = 1.5. Find real depth.
Solution:
Real depth = Apparent depth × Refractive index = 15 × 1.5 = 22.5 cm
- A light ray travels from water (n = 1.33) to glass (n = 1.5) with angle of incidence = 30°. Find angle of refraction.
Solution:
1.33 × sin 30° = 1.5 × sin r
0.665 = 1.5 × sin r → sin r = 0.4433 → r = 26.3°
- A ray of light from glass to water strikes at angle 60°. Critical angle is 48°. Will Total Internal Reflection occur?
Solution:
Yes, since 60° > 48°. Yes, Total Internal Reflection occurs.
- In a prism, angle of prism = 60°. Minimum deviation = 30°. Calculate refractive index.
Solution:
n = sin[(A + D)/2] / sin(A/2) = sin(45°)/sin(30°) = 0.7071/0.5 = 1.414
- A prism deviates light by 40°. Angle of incidence = 50°, prism angle = 60°. Find angle of emergence.
Solution:
Deviation = i + e – A → 40 = 50 + e – 60 → e = 50°
Answer: 50°
- A ray in water bends away from the normal on entering air. Why?
Solution:
Because speed of light increases and refractive index decreases. Light travels faster in air than in water.
- A light ray in air strikes a prism at 45° and emerges at 65°. If the prism angle is 60°, calculate the deviation.
Solution:
Deviation = i + e – A = 45 + 65 – 60 = 50°
- A coin appears 20 cm deep in a tank. If refractive index of water is 1.33, find actual depth.
Solution:
Real depth = 20 × 1.33 = 26.6 cm
- A medium has speed of light = 2.25 × 10⁸ m/s. What is its refractive index?
Solution:
n = 3 × 10⁸ / 2.25 × 10⁸ = 1.33
- Calculate the speed of light in a medium of refractive index 1.8.
Solution:
Speed = 3 × 10⁸ / 1.8 = 1.67 × 10⁸ m/s
- A prism has a refractive index of 1.5 and angle of prism is 60°. Find minimum angle of deviation.
Solution:
Using n = sin[(A + D)/2] / sin(A/2), solve for D:
1.5 = sin[(60 + D)/2] / sin 30 → sin[(60 + D)/2] = 0.75 → (60 + D)/2 = 48.6° → D = 37.2°
- If angle of incidence in water is 50° and angle of refraction in air is 70°, find refractive index of water.
Solution:
n = sin i / sin r = sin 50° / sin 70° = 0.766 / 0.940 = 0.815
- A diver sees the sun at an apparent angle of 30° from the vertical. Refractive index of water is 1.33. Find the real angle.
Solution:
sin i = n × sin r = 1.33 × sin 30° = 1.33 × 0.5 = 0.665
i = sin⁻¹(0.665) = 41.8°
- A glass block is 6 cm thick. Lateral shift observed is 2 cm. Find angle of refraction if angle of incidence is 60°.
Solution:
Using formula for lateral shift: Shift = t sin(i – r) / cos r
Given: shift = 2, t = 6, i = 60°
Trial method gives r ≈ 35° (approximate by substitution)
- Light takes 1.5 ns to pass through a medium of 45 cm thickness. Find speed of light in medium.
Solution:
Speed = distance / time = 0.45 / (1.5 × 10⁻⁹) = 3 × 10⁸ m/s
- A ray travels from medium A to B with i = 50°, r = 30°. Find n₂/n₁.
Solution:
n₂/n₁ = sin i / sin r = sin 50° / sin 30° = 0.766 / 0.5 = 1.532
- Refractive index of a material is 1.6. What is the angle of incidence for which angle of refraction is 30°?
Solution:
sin i = n × sin r = 1.6 × sin 30° = 1.6 × 0.5 = 0.8 → i = sin⁻¹(0.8) = 53.1°
- Speed of light in a plastic block is 2 × 10⁸ m/s. What is its refractive index?
Solution:
n = 3 × 10⁸ / 2 × 10⁸ = 1.5
- Find angle of incidence if angle of refraction is 45° and refractive index = 1.41.
Solution:
sin i = n × sin r = 1.41 × sin 45° = 1.41 × 0.707 = 0.997 → i = sin⁻¹(0.997) = 85.6°
- Light passes from glass (n = 1.5) into air. What is the maximum angle of incidence for which no refraction occurs (i.e., Total Internal Reflection)?
Solution:
Critical angle C = sin⁻¹(1 / 1.5) = sin⁻¹(0.6667) = 41.8°
- A pencil appears bent in water. If real depth is 12 cm and apparent depth is 9 cm, find refractive index.
Solution:
n = Real / Apparent = 12 / 9 = 1.33
- Time taken by light to cross a 60 cm thick slab of glass is 3 × 10⁻⁹ s. Find speed of light in glass.
Solution:
Speed = 0.6 / (3 × 10⁻⁹) = 2 × 10⁸ m/s
- A ray is incident at 50° in a medium and refracts at 32° in another. Calculate the refractive index.
Solution:
n = sin 50° / sin 32° = 0.766 / 0.530 = 1.445
- A slab of thickness 4 cm shows a lateral shift of 1 cm. Angle of incidence = 45°. Estimate angle of refraction.
Solution:
Using shift formula: Shift = t sin(i – r) / cos r, estimate r by substitution. Approximate value: 29°
- Light enters a medium with refractive index 1.52. What is speed of light in that medium?
Solution:
Speed = 3 × 10⁸ / 1.52 ≈ 1.97 × 10⁸ m/s
- A ray bends towards the normal. What does this tell about the two media?
Solution:
It travels from a rarer to a denser medium. Medium 2 has higher refractive index.
- Apparent depth of a stick in oil is 7 cm. If refractive index is 1.4, find real depth.
Solution:
Real depth = Apparent × Refractive index = 7 × 1.4 = 9.8 cm
- A slab of width 5 cm causes a lateral shift of 1.2 cm. Angle of incidence is 60°. Estimate angle of refraction.
Solution:
Estimate using shift = t sin(i – r)/cos r. Substituting and trial: r ≈ 34°
- A diver sees a fish at 1.2 m. Actual depth is 1.6 m. Find refractive index.
Solution:
n = Real / Apparent = 1.6 / 1.2 = 1.33
- In which medium does light travel faster: n = 1.45 or n = 1.65?
Solution:
Lower n means higher speed. n = 1.45
- A laser beam in water bends at 25° in air. If incidence angle is 18°, find refractive index of water.
Solution:
n = sin r / sin i = sin 25° / sin 18° = 0.4226 / 0.3090 = 1.367
- Light bends away from the normal when entering from medium A to B. Which is denser?
Solution:
Since it bends away, it enters a rarer medium. Medium A is denser.
- What happens to speed and wavelength of light when it enters a denser medium?
Solution:
Both decrease. Speed and wavelength decrease.
- Refractive index of diamond = 2.42. What is its critical angle?
Solution:
sin C = 1/2.42 = 0.4132 → C = sin⁻¹(0.4132) = 24.4°
- Light in air has wavelength 600 nm. Find its wavelength in glass (n = 1.5).
Solution:
Wavelength = 600 / 1.5 = 400 nm
- If angle of refraction = 90°, what is the angle of incidence called?
Solution:
Critical angle
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