An alternating voltage E = 200 sin 300 t is applied across a series combination of R = 10 Ω and an inductor 800 mH. The power factor of the circuit is
0.022
0. 065
0.042
0. 084
The inductance of a coil is directly proportional to
its length
the number of turns
the resistance of the coil
the square of the number of turns
The time constant of C - R circuit is
1/CR
C/R
CR
R/C
A 100 mH coil carries a current of 1 A. Energy stored in the magnetic field is
0.5 J
I J
0.1 J
0.05 J
A L-C circuit is in a state of resonance. If C = 0.1 μF and L = 0.25 H, then neglecting the ohmic resistance of the circuit, find the frequency of oscillations.
1007 Hz
100 Hz
109 Hz
500 Hz
A rectangular coil of 20 turns and area of cross-section 25 cm2 has a resistance of 100 Ω. If a magnetic field which is perpendicular to the plane of the coil changes at the rate of 1000 T per second, the current in the coil is
1 A
50 A
0. 5 A
5 A
Energy needed to establish an alternating current I in a coil of self inductance L is
L di/dt
Zero
LI2/2
IL2/2
In an AC circuit, the rms value of current, irms is related to the peak current, i0 by the relation
irms = √2i0
irms = πi0
irms = i0/π
irms = 1/√2 i0
A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is approximately
30%
50%
90%
10%
An alternating voltage V = 200√2 sin (100t) is connected to a 1μF capacitor through an AC ammeter. The reading of the ammeter shall be
10 m
20 mA
40 mA
80 mA
