Question

In a series LR circuit, the voltage drop across the inductor is 8 volt and across the resistor is 6 volt. The voltage applied and the power factor of the circuit respectively are

• A. 14 V, 0.8
• B. 10 V, 0.8
• C. 10 V, 0.6
• D. 14 V, 0.6

Answer 1

Answer: (C)

10 V, 0.6

The phase vectors of a resistor and an inductor make an angle of 90 degree with each other. Hence the net voltage will be obtained by taking the vector sum: $V_{net}=\sqrt{V_r^2+V_l^2}=\sqrt{36+64}=10V$
The power factor defined as the ratio of true power to apparent power will be given by $\frac{V_r}{V}$ since the current flowing through the inductor and resistor is the same. Power factor $=\frac{6}{10}=0.6$