Question

When an a.c. voltage is applied across series combination of a resistance R and an inductor of

inductance 2 milli Henry, the phase difference between current and applied voltage is $\frac{\pi }{6}$ radian.

When same a.c. voltage is applied across series combination of same resistance and a condenser of

capacity , $5\mu F$ the phase difference between current and applied voltage is $\frac{\pi }{3}$ radian. The value of

R is

• A. 10 Ω
• B. 20 Ω
• C. 40 Ω
• D. 50 Ω

Answer 1

The correct option is B

20 Ω

In case of L – R combination,

$tan\varphi =\frac{X_L}{R}=\frac{\omega L}{R}$

In case of C – R combination,

$tan\varphi =\frac{X_C}{R}=\frac{1}{\omega CR}$