- A simple LR circuit is connected to a battery at time
t = 0. e energy stored in the inductor reaches half
its maximum value at time
(a) R
L
ln^2
21 −
^ (b)
L
R
ln^21
2
−
(c)
L
R
ln
2
21 −
^ (d)
R
L
ln
21
2
−
- Power factor of an LR series circuit is 0.6 and that
of a CR series circuit is 0.5. If the element (L, C, and
R) of the two circuits are joined in series the power
factor of this circuit is found to be 1. e ratio of
the resistance in the LR circuit to the resistance in
the CR circuit is
(a)
6
5
(b)
5
6
(c)
4
33
(d)
33
4
- Determine the rms value of
a semi-circular current wave
which has a maximum value
of a.
(a) (/ 12 )a (b) (/ 32 )a
(c) (/ 23 )a (d) (/ 13 )a
- A 50 W, 100 V lamp is to be connected to an ac
mains of 200 V, 50 Hz. What capacitor is essential
to be put in series with the lamp?
(a)
25
2
μF (b)
50
π 3
μF
(c)
50
2
μF (d)
100
π 3
μF
- A coil having 500 square loops each of side 10 cm is
placed normal to a magnetic eld which increased at
a rate of 1.0 T s–1. Find the induced e.m.f. (in volt).
(a) 50 V (b) 1 V (c) 10 V (d) 5 V
- In a circuit shown in gure, A and B are two cells of
same emf E but di erent internal resistances r 1 and
r 2 (r 1 > r 2 ), respectively. Find the value of R such
that potential di erence across the terminals of cell
A is zero a long time a er key K is closed.
R R L
EE
r 1 r 2
R
R
R
R
K
C
y
0
(a)^2
3 12
()rr−^ (b)^3
2 12
()rr−
(c)^3
4 12
()rr−^ (d)
4
3 12
()rr−
- In the circuit shown in gure, key K is closed at
t = 0, the current through the key at the instant
t = 10–3 ln 2s is
4 :
K
L = 5 mH
C = 0.1mF
5 :
6 :
5 :
20V
(a) 2A (b) 3.5A (c) 2.5A (d) 0
- In an LR series circuit, a sinusoidal V = V 0 sin Zt
is applied. It is given that L = 35 mH, R =11:,
Vrms = 220 V, Z/2p = 50 Hz and p = 22/7. Find the
amplitude of the current in steady state and obtain
the phase di erence between the current and the
voltage.
(a) 20
4
A,
π
(b) 2
6
A,
π
(c) 2
4
A,
π
(d) 2
3
A,
π
- A bulb is rated at 100V, 100W. It can be treated as
a resistor. Find out the inductance of an inductor
(called choke coil) that should be connected in series
with the bulb to operate the bulb at its rated power
with the help of an ac source of 200 V and 50 Hz.
(a)
π
3
H (b)^3
π
H (c) 2H (d) 3H
- e equivalent inductance between A and B is
(a) 1 H (b) 4 H (c) 0.8 H (d) 16 H
- An alternating emf of angular frequency Z is applied
across an inductance. The instantaneous power
developed in the circuit has an angular frequency
(a) ω
4
(b)
ω
2
(c) 2Z (d) 4Z
- e magnetic ux through a coil varies with time
as φ = 5t^2 + 6t + 9. e ratio of emf at t = 3 s to
t = 0 s will be
(a) 1 : 9 (b) 1 : 6 (c) 6 : 1 (d) 9 : 1
