Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A: Alloys such as constantan and manganin are used in making standard resistance coils. Reason R: Constantan and manganin have very small value of temperature coefficient of resistance. In the light of the above statements, choose the correct answer from the options given below.

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

Both A and R are true but R is NOT the correct explanation of A.

Current Electricity PYQ — JEE Main 2022 · 29 Jul · Shift 2 · Q47 with Solution

View written solutionFree

Correct answer: A

Understand the assertion

Assertion A: Alloys such as constantan and manganin are used in making standard resistance coils.

This is true. In electrical measurements, standard resistance coils are made from materials whose resistance remains nearly constant with change in temperature. Constantan and manganin are commonly used for this purpose.
Understand the reason

Reason R: Constantan and manganin have very small value of temperature coefficient of resistance.

This is also true. Their temperature coefficient of resistance is very small, so even if temperature changes slightly, the resistance changes very little.
Check whether R explains A

For a standard resistance coil, we need resistance to remain stable and reproducible. If the temperature coefficient is very small, then:

$R_T \approx R_0(1 + \alpha \Delta T)$

where $\alpha$ is the temperature coefficient of resistance.

Since for constantan and manganin, $\alpha$ is very small, the change in resistance with temperature is negligible. Hence they are suitable for making standard resistance coils.

Therefore, R is the correct explanation of A.
Evaluate options
- 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. ❌
Final conclusion

The correct option is A.

View written solutionFree

Correct answer: A

Understand the assertion

Assertion A: Alloys such as constantan and manganin are used in making standard resistance coils.

This is true. In electrical measurements, standard resistance coils are made from materials whose resistance remains nearly constant with change in temperature. Constantan and manganin are commonly used for this purpose.
Understand the reason

Reason R: Constantan and manganin have very small value of temperature coefficient of resistance.

This is also true. Their temperature coefficient of resistance is very small, so even if temperature changes slightly, the resistance changes very little.
Check whether R explains A

For a standard resistance coil, we need resistance to remain stable and reproducible. If the temperature coefficient is very small, then:

$R_T \approx R_0(1 + \alpha \Delta T)$

where $\alpha$ is the temperature coefficient of resistance.

Since for constantan and manganin, $\alpha$ is very small, the change in resistance with temperature is negligible. Hence they are suitable for making standard resistance coils.

Therefore, R is the correct explanation of A.
Evaluate options
- 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. ❌
Final conclusion

The correct option is A.