18

ELECTROMAGNETIC
INDUCTION
AND
ALTERNATING
CURRENTS
( Answers
at
the
end
of
all
questions )
Page
1
1 )
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
µ
F
( b )
4
µ
F
( c )
2
µ
F
( d )
1
µ
F
[ AIEEE
2005 ]
2 )
The
phase
difference
between
the
alternating
current
and
emf
is
π /
2.
Which
of
the
following
cannot
be
the
constituent
of
the
circuit ?
( a )
R, L
( b )
C
alone
( c )
L
alone
( d )
L, C
[ AIEEE
2005 ]
3 )
A
circuit
has
a
resistance
of
12
ohm
and
an
impedance
of
15
ohm.
The
power
factor
of
the
circuit
will
be
( a )
0.4
( b )
0.8
( c )
0.125
( d )
1.25
[ AIEEE
2005 ]
4 )
A
coil
of
inductance
300
mH
and
resistance
2
Ω
is
connected
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 )
0.3 s
( d )
0.15 s
[ AIEEE
2005 ]
5 )
In
an
LCR
series
a.c.
circuit,
the
voltage across
each
of
the
components,
L,
C
and
R
is
50 V.
The
voltage
across
the
LC
combination
will
be
( a )
50 V
( b )
50
√
2 V
( c )
100 V
( d )
0 V
( zero )
[ AIEEE
2004 ]
6 )
A
coil
having
n
turns
and
resistance
having
R
Ω
is
connected
with
a
galvanometer
of
resistance
4R
Ω
.
This
combination is
moved
in
time
t
seconds
from
a
magnetic
field
W
1
weber
to
W
2
weber.
The
combined
current
in
the
circuit
is
( a )
5Rnt
W
W
1
2

( b ) 
5Rt
)
W
W
(
n
1
2

( c )
Rnt
W
W
1
2


( d )
Rt
)
W
W
(
n
1
2


[ AIEEE
2004 ]
7 )
In
a
uniform
magnetic
field
of
induction
B,
a
wire
in
the
form
of
semicircle
of
radius
r
rotates
about
the
diameter
of
the
circle
with
angular
frequency
ω
.
The
axis
of
rotation
is
perpendicular
to
the
field.
If
the
total
resistance
of
the
circuit
is
R,
the
mean
power
generated
per
period
of
rotation
is
( a )
2R
r
B
2
ω
π
( b )
8R
)
r
B
(
2
2
ω
π
( c )
2R
)
r
B
(
2
ω
π
( d )
8R
)
r
B
(
2
2
ω
π
[ AIEEE
2004 ]
8 )
In
an
LCR
circuit,
capacitance
is
changed
from
C
to
2C.
For
the resonant
frequency
to
remain
unchanged,
the
inductance
should
be
changed
from
L
to
( a )
4 L
( b )
2 L
( c )
L
/
2
( d )
L
/
4
[ AIEEE
2004 ]
9 )
A
metal
conductor
of
length
1
m
rotates
vertically
about
one
of
its
ends
at
angular
velocity
5
radians
per
second.
If
the
horizontal
component
of
earth’s
magnetic
field
is
0.2 × 10

4
T,
then
the
emf
developed
between
the
two
ends
of
the
conductor
is
( a )
5
µ
V
( b )
50
µ
V
( c )
5
mV
( d )
50
mV
[ AIEEE
2004 ]
10 )
The
magnetic
flux
linked
with
a
coil
is
given
by
the
equation
φ
=
3t
2
+
4t
+
9
Wb.
The
magnitude
of
induced
emf
at
t
=
2
sec.
is
( a )
16 V
( b )
9 V
( c )
4 V
( d )
1 V
[ AIEEE
2003 ]
11 )
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 selfinduction
in
the
coil
is
( a )
0.1 H
( b ) 0.2 H
( c )
0.4 H
( d )
0.8 H
[ AIEEE
2003 ]
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View Full Document18

ELECTROMAGNETIC
INDUCTION
AND
ALTERNATING
CURRENTS
( Answers
at
the
end
of
all
questions )
Page
2
12 )
Two
coils
are
placed
close
to
each
other.
The
mutual
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 Spring '06
 Smith
 Capacitance, Current, Inductance, Power, Magnetic Field, Inductor, Alternating Currents

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