QUEST
TUTORIALS
Head Office
: E16/289, Sector8, Rohini, New Delhi, Ph. 65395439
Q1.
A wheel with 10 metals spokes each 0.50 m long is rotated with a speed of 120 rpm in a plane normal to the earth’s
magnetic field of 0.04 mT. The induced e.m.f. between the axle and the rim of the wheel will be
(a) 6.28
×
10

4
V
(b) 6.28
×
10

5
V
(c) 6.28
×
10

6
V
(d) 6.28
×
10

3
V
Q2.
A toroidal solenoid with an air core has an average radius of 15 cm, area of cross section 12 cm
2
, and 1200 turns.
Ignoring the field variation across the cross section of the toriod, the self inductance of the toriod will be
(a) 2.3
×
10

2
mH
(b) 2.3
×
10

1
mH
(c) 2.3 mH
(d) 23 mH
Q3.
The energy stored in an inductor of self inductance L, in which a current of I amps flows is given by
(a) 1/2 LT
2
(b) 1/2 IL
2
(c) 1/2 LI
(d) 1/2 L
2
I
2
Q4.
A jet plane is traveling west at the speed of 1800 kmph. The induced e.m.f. developed between the ends of its wings 25
m long at a place where the earth’s magnetic field has a magnitude of
(a) 5
×
10

4
T
(b) 3.1
×
10

2
V
(c) 0.31 V
(d) 3.1 V
Q5.
A small resistor usually put in parallel to the current carrying coil of an electromagnet to
(a) increase the current through the coil of electromagnet
(b) decrease the current through the coil of electromagnet
(c) increase the induced voltage across the coil of the electromagnet
(d) decrease the induced voltage across the coil of electromagnet
Q6.
An electron moves in a circle with uniform speed in a stationary magnetic field normal to the plane of the circle. If the
magnitude of the field is made to increase with time, the electron will
(a) speed up in the same orbit
(b) speed down in the same orbit
(c) speed up in an orbit of higher radius
(d) speed down in an orbit of lower radius
Q7.
The Lorentz force acting on a charge q coulombs, moving with a velocity V
a
in an electric
( )
E
a
and magnetic
( )
B
a
field
mutually perpendicular to each other, is given by
(a)
( )
[ ]
V
B
E
q
F
a
a
a
a
×
+
=
(b)
( )
[ ]
B
V
E
q
F
a
a
a
a
×
+
=
(c)
( )
[ ]
E
V
B
q
F
a
a
a
a
×
+
=
(d)
( )
[ ]
V
E
B
q
F
a
a
a
a
×
+
=
Q8.
The mutual inductance between two coils of wire each of length
l
, and turns per unit length n, area of cross section of
windings ‘a’ is given by
(a)
μ
0
n
2
l
a
(b)
μ
0
n
l
a
(c)
μ
0
n
l
a
2
(d)
μ
0
n
l
2
a
Q9.
The SI unit of self
(mutual) inductance is
(a) Tesla
(b) Weber/m
2
(c) Henry
(d) Weber/Amp
2
Q10.
Formula for the self inductance of a solenoid of length
l
, area of cross section’a’, and the number turns per unit length
n, is
(a)
μ
0
n
l
a
2
(b)
μ
0
n
l
2
a
(c)
μ
0
n
2
l
a
(d)
μ
0
n
2
2
l
a
2
Q11.
Formula for the self inductance of a solenoid of length
l
, area of cross

section ‘a’, and the number turns per unit
length n, is
(a)
μ
0
n
l
a
2
(b)
μ
0
n
l
2
a
(c)
μ
0
n
2
l
a
(d)
μ
0
n
2
2
l
a
2
Q12.
In a ‘step down’ transformer the turns ratio
(a) has to be less than 1
(b) has to be equal to 1
(c) has to be greater than 1
(d) can be any value
Q13.
A bar falling vertically through the hollow region of a thick cylindrical copper shell, experiences a strong retarding
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 Spring '11
 Grimaldi
 Physics, Current, Inductor, New Delhi, LC circuit, pH., series a.c. circuit

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