HOTs on AC for class XII

ALTERNATJNG CURRENT (2 Marks)

Q1.         Mention the factors on which the resonant frequency of a series LCR-circuit depends. Plot a graph showing variation of impedence of a series LCR-CIRCUIT with the Frequency of the applied a.c. source.

Q2.         A 50 W – 100 W electric bulb is to be used on a 200 V -  50  Hz a. c. supply. Calculte the inductance of the lamp so that it may glow with its normal brightness.(Take pie = 3 )

Q3.         In an a.c circuit A the current leads the voltage by 30⁰ and in circuit B the current lags voltage by 30⁰. What is the ratio of their power factors?

ALTERNATJNG CURRENT (3 Marks)

Q1.      200V variable frequency a.c source is connected to a series combination of L=5H, C=80 μF, and R=40 Ω Calculate (i) angular frequency of the source to get maximum current in the circuit, (ii) the current amplitude at the resonance and (iii) the power dissipation in the circuit.

Q2.      A coil draws a current of 1.0 A and a power of 100 W from an a.c. source of 110 V and 50 Hz. Find the resistance and the inductance of the coil.

Q3.      A resistance of 40 Ω is connected to an a.c. source of 220 V, 50 Hz. Find (i) the rms current (ii) the maximum instantaneous current in the resistor and (iii) the time taken by the current to change from its maximum value to the rms value.