Answer to Question #200534 in Electric Circuits for Shani

Question

A series R-L circuit is connected to 110V ac source.If voltage across resistor is 85V ,find power dissipated in circuit

Answer 1

Since the voltages across the inductor and the resistor are 90° out of phase, we obtain the voltage across the inductor in the phase domain as follows: If the voltage across the resistor is V₁

The voltage across the inductor will be jV₂

​

. Assume the voltage of the source is V₃

Applying kvL law

$$V_1+jV_2=V_1cos(wt)+V_2sin(wt)=V_3cos(wt-\theta)=85+V_2sin(wt)=110cos(wt-\theta)$$

$110=\sqrt{85^2+V_2^2}$

​ $V_2=69.82V$

For example

$P_{ave}=\frac{1}{2}\frac{V_R^2}{R}$

Assume

$R=20 ohm$

And V_R=85 V

Put value

$P_{av}=\frac{1}{2}\frac{85^2}{20}=180.6 W$