Question

a. Draw graphs showing the variations of inductive reactance and capacitive reactance with frequency of applied ac source.

b. Draw the phasor diagram for a series LRC circuit connected to an AC source.

c. When an alternating voltage of 220V is applied across a device X, a current of 0.25A flows which lags behind the applied voltage in phase by π/2 radian. If the same voltage is applied across another device Y, the same current flows but now it is in phase with the applied voltage.

(i) Name the devices X and Y.

(ii) Calculate the current flowing in the circuit when the same voltage is applied across the series combination of X and Y.

Answer 1

(a)

(b)

(c) (i) In device X, Current lags behind the voltage by π /2, X is an inductor In device Y, Current in phase with the applied voltage, Y is resistor

(ii) We are given that

0.25=220/XL, XL =880Ω, Also 0.25=220/R, R = 880Ω

For the series combination of X and Y,

Equivalent impedance Z = 880 √2 Ω , I= 0.177 A.