Question

Given below are two statements.

Assertion : In an LR series circuit in AC , current in the circuit will decrease with increase in frequency.

Reason : Phase difference between current function and voltage function will increase with increase in frequency.

Based on these statements, choose the correct alternative.

• A. Both the assertion and reason are correct, and reason is the correct explanation of assertion.
• B. Both the assertion and reason are correct, but reason is not the correct explanation of assertion.
• C. Assertion is correct, but reason is incorrect.
• D. Assertion is incorrect, but reason is correct.

Answer 1

The correct option is B Both the assertion and reason are correct, but reason is not the correct explanation of assertion.

We know that,

$I=\frac{V}{Z}=\frac{V}{\sqrt{R^2+X_L^2}}=\frac{V}{\sqrt{R^2+(2\pi fL{)}^2}}$

$\Rightarrow$ With increase in frequency, current decreases.

Also,

$\tan \varphi =\frac{X_L}{R}=\frac{2\pi fL}{R}$

$\Rightarrow$ With increase in frequency, $\tan \varphi$ and therefore $\varphi$ will increase.

Therefore, both the assertion and reason are correct, but reason is not the correct explanation of assertion.

Hence, option $\left(B\right)$ is the correct answer.