Question

a 12ohm resistor and a 0.21H inductor are connected in series to an ac source operating at 20V, 50cycle/second . the phase angle between current and source voltage is

1) 30degree

2) 40

3) 80

4) 90

Answer 1

The phase angle between the current and the voltage is,
$\phi ={\tan }^{-1}\frac{\omega L}{R}$
Here,
$\omega =2\pi f=2\pi \times 50=100\pi rad/s$
So,
$\phi ={\tan }^{-1}\left(\frac{100\pi \times 0.21}{12}\right)=79.69degree$
So 3 is the right choice.