JEE Main 2024 · 27 January · evening · Single correct · +4 / −1
Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : In Vernier calliper if positive zero error exists, then while taking measurements, the reading taken will be more than the actual reading.
Reason (R) : The zero error in Vernier Calliper might have happened due to manufacturing defect or due to rough handling.
In the light of the above statements, choose the correct answer from the options given below :
- (a) Both (A) and (R) are correct and (R) is the correct explanation of (A)
- (b) Both (A) and (R) are correct 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 and solution
Answer (b) Both (A) and (R) are correct but (R) is not the correct explanation of (A)
Solution
Physics sir · 4 steps
Both statements are true, but does the cause of an error explain which way it shifts the reading?
- Positive zero error. With the jaws closed, the vernier zero sits to the right of the main scale zero. So the instrument already shows a positive reading when the true length is zero.
- Check Assertion. That extra amount is added to every measurement, so the observed reading is more than the actual length. We correct it by subtracting the error. (A) is true.
Actual reading = Observed reading - (positive zero error)
- Check Reason. Zero error comes from a manufacturing defect or from rough handling that wears or bends the jaws. (R) is true. But (R) only says where the error comes from. It says nothing about why a positive error makes the reading too large.
- So. Both statements are correct, but (R) is not the explanation of (A). The answer is (b).
The idea to keep. In assertion-reason questions, test the link separately. A reason that is true and on the same topic still fails if it does not answer the "why" behind the assertion.
Answer from the NTA final answer key. Solution by PrepWiser.