Question

If the frequency is halved and the resistance is doubled, the impedance of a series RL circuit :

• A. doubles
• B. remains constant
• C. halves
• D. cannot be determined without values

Answer 1

The correct option is D cannot be determined without values

Impedance, $X=\sqrt{R^2+{\omega }^2{L}^2}$

${\omega }^{{}^{\prime }}=\frac{\omega }{2}$ and $R^{{}^{\prime }}=2R$

Hence, $X^{{}^{\prime }}=\sqrt{4R^2+\frac{{\omega }^2{L}^2}{4}}$

Hence, without values of $R,\omega ,L$, we can,t determine the change in impedance.

Answer-(D)