Alternating Current

A multimeter reads a voltage of a certain AC source as 100 V. What is the peak value of voltage of AC source ?

• 200 V

• 100 V

• 141 V

• 400 V

A senes LCR circuit contains inductance 5 mH, capacitance 2 μF and resistance 10 Ω. If a frequency AC source is varied, what is the frequency at which maximum power is dissipated ?

• $\frac{{10}^5}{\mathrm{\pi }} \mathrm{H}$

• $\frac{{10}^{-5}}{\mathrm{\pi }} \mathrm{Hz}$

• $\frac{2}{\mathrm{\pi }} \times {10}^5 \mathrm{Hz}$

• $\frac{5}{\mathrm{\pi }} \times {10}^3 \mathrm{Hz}$

A step down transformer has 50 turns on secondary and 1000 turns on primary winding. If a transformer is connected to 220 V, 1 A AC source, what is output current of the transformer ?

• $\frac{1}{20} \mathrm{A}$

• 20 A

• 100 A

• 2 A

The average power dissipated in AC circuit is 2 W. If a current flowing through a circuit is 2 A impedance is 1 Ω, what is the power factor of the AC circuit ?

• 0.5

• 1

• Zero

• $\frac{1}{\sqrt{2}}$

A transformeris used to light 100 W -110 V lamp from 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is

• 96 %

• 90 %

• 99 %

• 95 %

In an L-C-R circuit, at resonance

• the current is minimum

• the current and voltage are in phase

• the current leads the voltage by $\frac{\mathrm{\pi }}{2}$

• the impedance is maximum

The average power dissipated in a pure inductor is

• $\frac{{\mathrm{Vl}}^2}{4}$

• $\frac{1}{2} \mathrm{Vl}$

• Zero

• Vl²

The rms value of current in a 50 Hz AC circuit is 6 A. The average value of AC current over a cycle is

• $6\sqrt{2}$

• $\frac{3}{\mathrm{\pi }/\sqrt{2}}$

• Zero

• $\frac{6}{\mathrm{\pi }\sqrt{2}}$

In a series L-C-R circuit, the potential drop across L, C and R respectively are 40 V, 120 V and 60 V. Then, the source voltage is

• 220 V

• 160 V

• 180 V

• 100 V

In a series L-C-R circuit, an alternating emf (V) and current (i) are given by the equation $\mathrm{V} = {\mathrm{V}}_0 \sin \mathrm{\omega t}, \mathrm{I} = {\mathrm{I}}_0 \sin \left(\mathrm{\omega t} + \frac{\mathrm{\pi }}{3}\right)$. The average power dissipated in the circuit over a cycle of AC is

• $\frac{{\mathrm{V}}_0{\mathrm{I}}_0}{2}$

• $\frac{{\mathrm{V}}_0{\mathrm{I}}_0}{4}$

• $\frac{\sqrt{3}}{2} {\mathrm{V}}_0{\mathrm{I}}_0$

• zero