A resistance of \(20~ \mathrm{ohms}\) is connected to a source of an alternating potential, \(V=220sin(100 \pi t).\) The time taken by the current to change from its peak value to its r.m.s value will be: 

1.	\( 0.2~ \mathrm{sec}\)	2.	\( 0.25~ \mathrm{sec}\)
3.	\(25 \times10^{-3}~ \mathrm{sec}\)	4.	\(2.5 \times10^{-3}~ \mathrm{sec}\)

An alternating current of frequency ‘f’ is flowing in a circuit containing a resistance R and a choke L in series. The impedance of this circuit will be:

1. R + 2πfL

2. $\sqrt{R^2+4{\pi }^2{f}^2{L}^2}$

3. $\sqrt{R^2+L^2}$

4. $\sqrt{R^2+2\pi fL}$

A resistance of 300 Ω and an inductance of $\frac{1}{\pi }$ henry are connected in series to an ac voltage of 20 volts and a 200 Hz frequency. The phase angle between the voltage and current will be:

1. ${\tan }^{-1}\frac{4}{3}$

2. ${\tan }^{-1}\frac{3}{4}$

3. ${\tan }^{-1}\frac{3}{2}$

4. ${\tan }^{-1}\frac{2}{5}$

In a region of uniform magnetic induction B = 10^–2 tesla, a circular coil of radius 30 cm and resistance π² ohm is rotated about an axis that is perpendicular to the direction of B and which forms a diameter of the coil. If the coil rotates at 200 rpm the amplitude of the alternating current induced in the coil is :

(1) 4π² mA

(2) 30 mA

(3) 6 mA

(4) 200 mA

In a LCR circuit having L = 8.0 henry, C = 0.5 μF and R = 100 ohm in series. The resonance frequency in radian per second is 

(1) 600 radian/second

(2) 600 Hz

(3) 500 radian/second

(4) 500 Hz

The impedance of a circuit consists of 3 ohm resistance and 4 ohm reactance. The power factor of the circuit is :

(1) 0.4

(2) 0.6

(3) 0.8

(4) 1.0

The power factor of a good choke coil is:

(1) Nearly zero

(2) Exactly zero

(3) Nearly one

(4) Exactly one

L, C and R represent physical quantities inductance, capacitance and resistance respectively. The combination representing the dimension of frequency will be:

1. LC

2. (LC)^–1/2

3. ${\left(\frac{{\displaystyle L}}{{\displaystyle C}}\right)}^{-1/2}$

4. $\frac{C}{L}$

In an ac circuit, a resistance of R ohm is connected in series with an inductance L. If the phase angle between voltage and current is 45°, the value of inductive reactance will be:

The phase difference between the current and voltage of LCR circuit in series combination at resonance is 

(1) 0

(2) π/2

(3) π

(4) –π