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18 - ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENTS
( Answers at the end of all questions )
1)
2
I
31
The self inductance of the motor of an electric fan is 10 H. In order to impart maximum
power at 50 Hz, it should be connected to a capacitance of
( a ) 8 I' F
( b I 4 I' F
( c I 2 I' F
( d I 1 I' F
[ AIEEE 2005 I
The phase difference between the alternating current and
following cannot be the constituent of the circuit ?
( a I R, L
( b I C alone ( c) L alone
( d I L, C
5)
In an LCR series a.c. circuit, the voltage across
50 V. The voltage across the LC
( a I 50 V
( b I so..J2 V
( c I 1oo V
A coil having n turns and resistance
resistance 4R n. This combination i
C~
~l:g
oh~ower factor of
I AIEEE
2005 I
the components, L, C and R is
o V I zero I
2R
I d I - _n(:...W_,2,_-_w_1'-'-l
Rt
[ AIEEE 2004 J
The axis of rotation
R, the mean power
ld.
tatlon is
r2 .... 12
I c I (Btr<O>)
8R
2004 I
n
Rnt
(aiB"r.,
I AIEEE
is connected with a galvanometer of
~in time t seconds from a magnetic field W 1
in the circuit is
w2 -w1
is perpendicular
generated per p oo
2
I
E 2005)
+
combinatio~~
(a I
8
AI
n is co~ed to a source of voltage 2 V.
The current reaches half of its steady state value In
(a ) 0.1 s
(b) 0.05 s
( c I 0.3 s
( d ) 0.1
I AIEEE 2005 I
A coil of inductance 300 mH and resistance 2
I
G':\;7
A circuit has a resistance of 12 ohm and an impedance of 15
the circuit will be
( a I 0.4
( b I 0.8
( c J 0.125
( d I 1.25
4)
6
Page 1
2R
2
[ AIEEE 2004 J
Id I
u it, capacitance is changed from C to 2C. For the resonant frequency to
anged, the inductance should be changed from L to
(b I 2 L
( c I L /2
( d I L /4
I AIEEE 2004 I
angular
field is
the two ends of the conductor is
( d I 50 mV
[ AIEEE 2004 J
10 1 The magnetic flux linked with a coil is given by the equation
magnitude of induced emf at t
2 sec. Is
( a 1 16 V
(b 1 9 V
(c ) 4V
(d 1 1V
=
11
t = 3t2 +
4t + 9 Wb. The
1AIEEE
2003 1
1 When the current changes from + 2 A to - 2 A in 0.05 second, an e .m .f. of 8 V is induced
in a coil. The coefficient of self-induction in the coil is
( a I 0.1 H
( b) 0.2 H
( c I 0.4 H
( d ) 0.8 H
[ AIEEE 2003)
18 - ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENTS
( Answers at the end of all questions )
12 )
Page 2
Two coils are placed close to each other. The mutual inductance of the pair of coils
depends upon
( a ) currents in the coils ( b ) materials of the wires of the coils
( c ) relative position and orientation of the coils
( d ) rates at which the currents are changing in the coils
003)
13)
is
(a I Q
(b
I Q/2
(c) Q/.J3
14 ) When number of turns in a coil is tripled, without
its self-inductance becomes
( a } on~third
( b ) three times
length of the coil,
[ AIEEE 2002 J
( c ) six
15 ) The equivalent inductance between
A and B is
(a}O
16
(b)1H
(c)3H
(d)9H
I The
[ AIEEE 2002 J
(a) zero
17) The core
laminated so as to
(a J
(c)
18
( b ) make it robust and strong
( d ) reduce the energy loss due to eddy current
) AIEEE 2002 )
•
I
number of turns in a primary coil are 140 and that in a secondary coil
urr.,nt in primary coil is 4 A, then that in the secondary coil is
(b) 2 A
( c} 6 A
( d} 10 A
[ AIEEE 2002 J
of capacitance 4 I' F and a resistor of 2.5 M.Cl are connected in series to a
of emf 12 volt having negligible internal resistance. Then time in which potential
across the capacitor will be three times the potential drop across the resistor will is
( a J 13.86 s
( b ) 6.93 s
(c
1 21.12
s
(d
1
3.46 s
)liT 2005 J
20 ) A long hollow cylindrical wire is placed parallel to the direction of uniform magnetic field
which is directed along + z-axls. Then Induced current on the surface of cylinder is
( a ) in the direction of the magnetic field
( c ) clockwise as seen from + z-axis
(b) zero
( d ) anticlockwise as seen from + z-axis
(liT 2005 J
18 - ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENTS
( Answers at the end of all questions )
21
Page 3
1 The variation of induced emf ( S 1 with time ( t 1
in a coil if a short bar magnet is moved along
its axis with a constant velocity is best represented
as
[liT 2004}
t
(a I
22 )
In an
RC
•
I bI
circuit while
I dI
ln I
s
doubled, which of the solid curve
of /n I versus time ?
(a) P
IbI
Q
R
Q
(c) R
p
t
23
I
i _
circuit
in series,
or
I
e
'
\
'
the two elements:
(b) R
(d) R
=1
=
k .0, C
1 k n, L
=1 !1F
=
1 H
[liT 2003[
p
Q
fill"'-'
-f-.J-""·
E
s
flows in Q.
IQ•
Then the direction
(as seen by E) are
( a ) respectively clockwise and anti-clockwise
( b 1 both clockwise ( c ) both anti-clockwise
( d ) respectively anti-clockwise and clockwise
[liT 2002}
18 - ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENTS
( Answers at the end of all questions )
25 )
A short-circuited coli Is placed In a time-varying magnetic field. Electrical power is
dissipated due to the current induced In the coil. If the number of turns were to be
quadrupled and the coil radius halved, the electrical power dissipated would be
(a) halved
26 )
Page 4
(b) the same
(c) doubled
( d ) quadrupled
An infinitely long conductor PQR is bent
to form a right angle as shown. A
current
I
flows through
PQR. The
magnetic field due to this current at the
M
-m - -
p
remaining
at M is now
given by
(a) 1/2
(c)2/3
27)
H2. The ratio
,R
(b} 1
(d)2
(111200~
A coil of wire having finite indu
e
d resistance has a conducting ring placed
coaxially within it. The coil Is c
cte t a battery at time t = 0, so that the time
dependent current It ( t ) st
ing through the coil. If 12 ( t ) is the current
induced in the ring, and
he magnetic field at the axis of the coil due to
11 ( t }, then as a function f
> 0 ), the product 12 ( t) · B ( t)
'?1.
~
( a ) increases with
( c ) does not vat)' w
28)
'·m
( b ) decreases with time
( d ) passes though a maximum.
[liT 2000)
,0.1
Two identical
ops of metal wire are lying on a table without touching each
other. Loop A ~a current which increases with time. In response, the loop B
( a)
stationary
(b)
fy the loop A
(c)
by the loop A
(d
its CM, with CM fixed
[Ill 1999)
inductance 8.4 mH and resistance 6 n is connected to a 12 V battery. The
the coil is 1.0 A at approximately the time
( b ) 20 s
( c ) 35 ms
(d) 1 ms
(Ill 1999)
small square loop of wire of side I is placed inside a large square loop of wire of
side L ( L >> I ). The loops are coplanar and their centres coincide. The mutual
inductance of the system is proportional to
2
2
(a) //1..
(b) 1 /L
(c) L/1
(d) 1.. 11
(Ill 1998)
31 )
L, C and R represent the physical quantities inductance, capacitance and resistance
respectively. The combinations which have the dimensions of frequency are
1
1
(b) ~
(c) - (d) C
[BIT 1992, Ill 1984)
(a) RC
L
~
L
18 - ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENTS
( Answers at the end of all questions )
32 )
Page 5
A metal rod moves at a constant velocity in a direction perpendicular to its length. A
constant uniform magnetic field exists in space in a direction perpendlcu lar to the rod
as well as its velocity. Select the correct statement (s) from the following:
( a ) the entire rod is at the same electric potential
( b ) there is an electric field in the rod
( c ) the electric potential is highest at the centre of the
its
ends
( d ) the electric potential is lowest at the centre of the
its
ends
(liT 1998)
33 ) A thin semicircular conducting ring of radius R is falling
its plane vertical In horizontal magnetic inductlon0
shown in the figure. At the position MNQ the spee
t
ring .is v and the potential difference developeo
rtng 1s
2
(a) zero
(b) BV1fR /2 and M is at r t )r. . t
ial
( c ) 1tBRV and Q Is at higher potential
( d ) 2RBV and Q is at higher potentia~ ...
)(
+
)(
B
X
X
N
X
X
X
[ liT 1996 1
34 ) Two different coils have self-induct
~ 8 mH, L21 2 mH. The current in one
coil Is increased at a constant
Th
urrent in the second coli is also increased at
the same constant rate. At a
tai
oint of time, the power given to the two coils is
the same. At that time, t r t ;
ure t,
e induced voltage and the energy stored in the
first coil are i1, v1 and
sp tively. Corresponding values for the second coli at
the s~me instant ar~e·
2
n
w2 respectively. Then
It
1
Wt
V2
1
(a)
4
4
(c) W2 : 4
(d) Vt "'4
(liT 19941
=
12"'
35 ) A
=
fll(
s
its
e
op of side L and resistance
e with a uniform velocity v
t~ one of its sides. A magnetic
in time and space, pointing
Into the plane of the loop exists
<Zl
<&>
B
("'
@
....
<&>
@ C8J
lY
v
figure )
induced in the loop is
~
~
<&l
~
BLv I R antlclockwise
2BLv /R anticlockwise
zero
36 )
(~
1<:9
(liT 1989)
<&l
<&>
<&l
<&l
~
~
A coli having an inductance of 1 /It henry Is connected in series with a resistance of
300 n. If 20 volts from a 200 cycles source are lm pressed across the combination, the
value of the tangent of the phase angle between the voltage and the current is
1
1
( a ) tan • ( 5 /4 )
( b ) tan " ( 4 /5 )
1
1
( c ) tan • ( 3 /4 )
( d ) tan • ( 4 /l )
( Roorkee 1980 1
18 - ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENTS
( Answers at the end of all questions )
37)
38 '
39)
Page 6
A circular coil of n turns and radius r is placed In a uniform magnetic field B.
Initially, the plane of the coil Is perpendicular to the field. The coil is rotated through
90•. Its resistance is R. The quantity of charge passing through the coil is
2
2
(a ) zero
( b} 11: n r B 1 R
( c) 2 • n r B 1 R
( d ) • n ,.2 B 1 R
A coil of insulated wire is connected in series with a bulb, a batter
When the circuit is completed, the bulb lights up immediately. The eire
is
and a rod of soft iron is placed inside the coil. On completing t t ) c '
observed that
( a ) the bulb is not so bright
( b ) there is a slight delay before the bulb lights up to its n C J ·
ness
( c ) the bulb is initially bright but gradually becomes dim
( d ) the bulb is brighter than before
An
L-C-R
series circuit is connected to an
witch.
ed off
extern~. t = 200 sin ( 1OOsl ).
The
values of the capacitance and resistance i n G c · are
1 p.F and
100 n
respectively. The amplitude of current in th
cir
will be maximum when the
inductance is
2
(a) 100 H
(b) 1001K H
(c) 1~
(d) 10000 H
=
=
=
40)
In series L-C·R circuit, e
eo sin cnt, 4 e : e u : 200 V, R
100 .n, L
0.1 H and
C
1 j.lf. The frequency of applie
~aries from 0 to co . For very low values of
frequency f, the amplitude of c
t i
(a) 2 A
(b) (11112) A
2
(d) zero
41)
flowing through an instrument in an a.c.
= 2 sin Clll: amperes. The power dissipated
=
(d) 2.5
I
42)
2.5
43)
w
=
w
100 sin ( 100 t-+ s 13) mA. The power
(d) 5.0
w
inductor and an electric bulb are connected in series to an a.c. supply
fre,qu1ency. As the frequency of the supply is increased gradually, then the
is found to
in brightness
:re~ise in brightness
'in1creas,e, reach maximum and then decrease in brightness
no change in brightness
A coil of resistance 200 n and self-inductance 1.0 H has been connected to an a.c.
source of frequency 100 IJI. Hz. The phase difference voltage and current is
( a ) 30•
( b ) 60•
( c ) 45•
( d ) 75•
45)
=
An alternating voltage E
200 112 sin (100 t) is connected to a 1
an a.c. ammeter. The reading of the ammeter shall be
( a ) 10 mA
( b ) 20 mA
( c } 40 mA
d ) 80 mA
Jl.f
capacitor through
18 - ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENTS
( Answers at the end of all questions 1
Page 7
46
I
A broadcasting centre broadcasts at 300 m band. A condenser of capacitance 2.4 J1F
is available. The value of the inductance required for the resonant circuit is
(a
47
I
I 10. 4
H
(b) 10. 8 H
(c
I 10. 6
H
(d
I 10. 2
H
It is desired to construct a circuit whose resonant frequency is
3 mH. The value of capacitor needed is about
(a 1 8.5 pico-farad
( b ) 0.8 picO-farad
( c 1 85 pico-farad
12
(pico
10" )
=
48
I
In series L·C·R circuit, the voltages across R, L and C
respectively. The voltage of the applied source is
(a 1 110 v
( b 1 10 v
( c 1 so v
( d 1 10 v
Answers
1
(d
~....,
v~O V
e,·
and 20 V

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