Assertion (A) : The unit used to measure speed is an example of a derived unit.

Reason (R) : Derived units can neither be changed nor can be related to any other fundamental unit.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false

Assertion (A) : Smaller the least count of an instrument, more precise the measurement made by using it.

Reason (R) : Least count of an instrument is the smallest measurement that can be taken accurately with it.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false

Assertion (A) : A pendulum clock goes slow (i.e., the time period of oscillation increases) when it is taken to mines.

Reason (R) : This is due to increase in the value of acceleration due to gravity g.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false

During a Physics practical, Ayush and Reema measured the length of a metal rod using two measuring instruments A and B. Ayush used instrument A and obtained a reading of 25.4 cm, while Reema used instrument B and obtained a reading of 25.36 cm.

(a) Why did Ayush and Reema get different values for the same length?

(b) Which measuring instrument is more accurate, A or B?

(c) Can you identify the measuring instruments A and B?

(d) Why is it important to use S.I. units while recording measurements?