ICSE – Grade 9 – Physics – Ch 01 – QA

1. Difference between Fundamental and Derived Quantities

Answer:
 Fundamental quantities are independent physical quantities that do not depend on any other quantity for their definition, such as length, mass, and time. Derived quantities, on the other hand, are obtained from the combination of two or more fundamental quantities, such as speed, force, and volume.

Example: Length (meter) is a fundamental quantity, while Speed (meter per second) is a derived quantity.

2. Difference between Fundamental and Derived Units

Answer:
 Fundamental units are the basic units used to measure fundamental quantities, such as meter (m) for length, kilogram (kg) for mass, and second (s) for time. Derived units are formed by combining fundamental units based on mathematical relationships, such as Newton (N) for force and Pascal (Pa) for pressure.

Example: The Newton (N) is derived as 1 N = 1 kg·m/s², which is obtained by combining the fundamental units of mass, length, and time.

3. Difference between Accuracy and Precision

Answer:
 Accuracy refers to how close a measured value is to the actual or true value, while precision refers to how consistently repeated measurements produce the same result, regardless of whether they are correct.

Example: If a student measures a length as 4.98 cm when the actual length is 5.00 cm, it is accurate. If the student gets 4.80 cm, 4.81 cm, and 4.82 cm repeatedly, it is precise but not accurate.

4. Difference between Systematic and Random Errors

Answer:
 Systematic errors occur due to faulty instruments, incorrect calibration, or observer bias, and they consistently affect measurements in the same direction. Random errors, on the other hand, occur unpredictably due to unknown variations in environmental conditions or observer mistakes.

Example: If a thermometer is incorrectly calibrated and always reads 2°C higher, it is a systematic error. If a student measures a length multiple times and gets slightly different values each time, it is a random error.

5. Difference between Parallax Error and Zero Error

Answer:
 Parallax error occurs when the observer’s eye is not aligned properly with the measuring scale, leading to incorrect readings. Zero error occurs when a measuring instrument does not start at exactly zero, causing all subsequent measurements to be incorrect.

Example: If a student reads a ruler at an angle instead of straight on, it results in a parallax error. If a Vernier caliper does not close properly and shows 0.02 cm when fully closed, it has a zero error.

6. Difference between Least Count and Resolution

Answer:
 Least count is the smallest measurement that an instrument can accurately record, while resolution refers to the ability of an instrument to distinguish between two closely spaced values.

Example: A Vernier caliper has a least count of 0.01 cm, meaning it can measure up to two decimal places. Resolution determines how small a change in measurement an instrument can detect.

7. Difference between Mass and Weight

Answer:
 Mass is the amount of matter in an object and remains constant everywhere in the universe. Weight is the force exerted by gravity on an object and varies based on the gravitational pull.

Example: A 1 kg object has the same mass on Earth and the Moon, but its weight will be different because the gravitational force on the Moon is weaker.

8. Difference between Speed and Velocity

Answer:
 Speed is the rate at which an object moves and is a scalar quantity, meaning it has only magnitude. Velocity is the speed of an object in a specific direction and is a vector quantity.

Example: A car moving at 60 km/h in any direction has speed, but if it moves 60 km/h towards the north, it has velocity.

9. Difference between Distance and Displacement

Answer:
 Distance is the total path traveled by an object, while displacement is the shortest straight-line distance from the starting point to the ending point.

Example: If a person walks in a circular path and returns to the starting point, the distance covered is the entire perimeter of the circle, but the displacement is zero.

10. Difference between Scalar and Vector Quantities

Answer:
 Scalar quantities have only magnitude, such as mass, speed, and time, whereas vector quantities have both magnitude and direction, such as force, velocity, and acceleration.

Example: A person running at 10 m/s is a scalar quantity, while a person running at 10 m/s east is a vector quantity.

11. Difference between Work and Energy

Answer:
 Work is the product of force and displacement in the direction of the force, while energy is the capacity to do work.

Example: When a person lifts a book, work is done against gravity. The person’s body converts chemical energy into mechanical energy to perform the work.

12. Difference between Work and Power

Answer:
 Work is the energy transferred when a force moves an object, whereas power is the rate at which work is done.

Example: If two people lift the same object, but one takes less time, that person exerts more power.

13. Difference between Force and Pressure

Answer:
 Force is a push or pull acting on an object, while pressure is the force applied per unit area.

Example: A sharp knife cuts better because it applies the same force over a smaller area, increasing the pressure.

14. Difference between Static and Dynamic Friction

Answer:
 Static friction acts when an object is at rest, preventing motion, while dynamic friction acts when an object is moving.

Example: A book on a table stays still due to static friction, but once pushed, it experiences dynamic friction.

15. Difference between Contact and Non-Contact Forces

Answer:
 Contact forces require physical interaction between objects, such as friction and tension, while non-contact forces act at a distance, such as gravity and magnetism.

Example: Pushing a door is a contact force, while the Earth pulling objects down is a non-contact force.

16. Difference between Kinetic and Potential Energy

Answer:
 Kinetic energy is the energy of motion, while potential energy is stored energy due to position.

Example: A moving car has kinetic energy, while a stretched bow has potential energy.

17. Difference between Elastic and Inelastic Collisions

Answer:
 Elastic collisions conserve kinetic energy, while inelastic collisions do not.

Example: A bouncing rubber ball has an elastic collision, while a lump of clay sticking to the floor has an inelastic collision.

18. Difference between Heat and Temperature

Answer:
 Heat is the total energy transferred between objects, while temperature measures the average kinetic energy of particles.

Example: A large bowl of warm water has more heat than a small cup of boiling water, but the cup has a higher temperature.

19. Difference between Conduction and Convection

Answer:
 Conduction transfers heat through direct contact, while convection transfers heat through fluid movement.

Example: A metal spoon in hot tea gets warm due to conduction, while hot air rising in a room is convection.

20. Difference between Reflection and Refraction

Answer:
 Reflection occurs when light bounces off a surface, while refraction occurs when light changes direction due to a change in medium.

Example: A mirror shows reflection, while a straw appears bent in water due to refraction.