Question

Assertion (A) Spring balance does not give correct measurement when it has been used for a long time.

Reason (R) Spring does not get longer time to regain its original configuration after use of long time.

• A. Both A and R are true and R is the correct explanation of A.
• B. Both A and R are true but R is not the correct explanation of A.
• C. A is true but R is false.
• D. A is false but R is true.

Answer 1

Answer: (A)

Both A and R are true and R is the correct explanation of A.

Answer 2

The question presents an Assertion (A) and a Reason (R) related to the functioning of a spring balance.

Assertion (A): Spring balance does not give correct measurement when it has been used for a long time.

This assertion is True. When a spring is used repeatedly over a long period, especially if subjected to stresses near or beyond its elastic limit, it undergoes a phenomenon called elastic fatigue. Elastic fatigue causes the material to lose its perfect elasticity. This can lead to the spring not returning to its original length (acquiring a permanent set or plastic deformation) or its spring constant changing. Both these effects would result in inaccurate measurements from the spring balance.

Reason (R): Spring does not get longer time to regain its original configuration after use of long time.

This statement is poorly phrased. Let's analyze its possible interpretations in the context of elastic fatigue:

1. If it means "the spring loses its ability to fully regain its original configuration (i.e., it acquires a permanent set), so the concept of needing more time for complete recovery becomes irrelevant": This interpretation aligns with the concept of elastic fatigue, where the spring suffers permanent deformation and does not return to its original state even if given infinite time. This would make the reason true and a correct explanation for the assertion. The NCERT text states: "The spring balance does not give correct measurement when it has been used for a long time. It is because the spring does not regain its original configuration completely after use of long time." This supports the idea of incomplete recovery due to long-term use (elastic fatigue).
2. If it means "the spring is not given enough time to regain its original configuration after each use": This refers to an operational issue rather than a material degradation over long-term use, and thus would not be the primary reason for a spring balance permanently losing accuracy after long use.
3. If it means "the spring becomes stiffer and takes less time to regain its configuration": This would also lead to incorrect measurements, but the reason's phrasing is still ambiguous.

Given the context from NCERT, the most plausible interpretation is that due to elastic fatigue from long-term use, the spring does not regain its original configuration completely. The phrasing "does not get longer time to regain its original configuration" is likely a convoluted way of expressing this permanent inability to fully recover. If the spring cannot fully regain its original configuration, it means it has a permanent deformation (permanent set), which directly causes the spring balance to give incorrect measurements. Therefore, Reason (R), when interpreted as permanent deformation due to elastic fatigue, is True and provides a correct explanation for Assertion (A).

Final conclusion: Both the Assertion and the Reason are true, and the Reason correctly explains the Assertion, assuming the interpretation that the spring loses its ability to completely regain its original configuration due to long-term use (elastic fatigue).

A spring balance loses accuracy over time due to elastic fatigue. Elastic fatigue is the degradation of a material's elastic properties after repeated stress cycles. This causes the spring to either not return completely to its original configuration (permanent set) or to change its elastic constant. Both effects lead to incorrect measurements. The reason states that the spring "does not get longer time to regain its original configuration after use of long time," which, while poorly phrased, implies that the spring does not fully recover its original shape due to long-term use (elastic fatigue), thus explaining the inaccuracy.