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Magnetic Effects of Current
1. A electron is moving on a circular path of radius r with speed v in a transverse magnetic field B. e/m
for it will be
(a)
(b)
(c) Bvr
(d)
2. In the given figure, the electron enters into the magnetic field. It deflects in …. direction.
Y
x
x
x
Xe
x
x
X
x
x
x
x
X
X
(a) + ve X direction
(b) – ve X direction
(c) + ve Y direction
(d) – ve Y direction
3. A charged particle of mass m and change q travels on a circular path of radius r that is perpendicular
To a magnetic field B. the time taken by the particle to complete one revolution is
(a)
(b)
(c)
(d)
4. A particle of mass m and charge q is released from rest at the origin as shown in the figure. The speed
Of the particle when it has travelled a distance d along the z-axis is given by
z
E0
B0
m, q
y
X
(a)
2qE0d
(b) q
M
(c)
E0d
B0
m
(d)
2m
qE0d
qE0d
5. Two wire of same length are shaped into a square and a circle. If they carry same current, ratio of the
magnetic moment is
(a) 2 : π
(b) π : 2
(c) π : 4
(d) 4 : π
6. Three long, straight and parallel wires carrying currents are arranged as shown in figure. The force
experienced by 10 cm length of wire Q is
R
Q
P
2 cm
20A
(a) 1.4 × 10-4 N towards the right
10 cm
10A
30A
(d) 2.6 × 10-4 N towards the left
(b) 1.4 × 10-4 N towards the left
(C) 2.6 × 10-4 N towards the right
7. A circular coil of 20 turns and radius 10 cm is placed in uniform magnetic field of 0. 10 T normal to the
plane of the coil. If the current in coil is 5 A, then the torque acting on the coil will be
(a) 31.4 Nm
(b) 3.14 Nm
(c) 0.314 Nm
(d) zero
8. A conducting loop carrying a current I is placed in a uniform magnetic field pointing into the paper as
shown. The loop will have a tendency to
B×
Y
I
X
(a) contract
(b) expand
(c) move towards +ve x-axis
(d) move towards -ve x-axis
9. A, B and C are parallel conductors of equal length carrying current I, I and 2i respectively. Distance
Between A and B is x. distance between B and C is also x. F1 is the force exerted by B on A. F2 is the
Force exerted by C on A. choose the correct answer
A
B
I
I
x
C
2I
x
(a) F1 = 2F2
(b) F2 = 2F1
(c) F1 = F2
(d) F1 = - F2
10. The rectangular coil of area A is in a field B. Find the torque about the z-axis when the coil lies
In the position shown and carries a current I
z
A
i
B
x
y
(a) I AB in negative z-axis
(b) IAB in positive z-axis
(c) 2 IAB in positive z-axis
(d) 2IAB in negative z-axis
11. If a current is speed through a spring, then the spring will
(a) expand
(b) compress
(c) remain
(d) None of these
12. The force between two long parallel wires A and B carrying current is 0.004 N/m. the conductors
Are 0.01 m apart. If the current in conductor A is twice that of conductor B, then the current in the
Conductor B would be
(a) 5 A
(b) 50 A
(c) 10 A
(d) 100 A
13. A current of 10 A is flowing in a wire of length 1.5 m. a force of 15 N acts on it when it is placed in a
Uniform magnetic field of 2 T. angle between the magnetic field and the direction of the current is
(a) 300
(b) 450
(c) 600
(d) 900
14. Consider the situation shown in figure. The straight wire is fixed but the can move under magnetic
f. The loop will
i1
i2
(a) remain stationary
(b) move towards the wire
(c) move away from the wire
(d) rotate about the wire
15. The strength of the magnetic field at a distance r near a long straight current carrying wire is B. the
Field at a distance
will be
(a)
(b)
(c) 2B
(d) 4C
16. A circular conductor, of uniform resistance per unit length, is connected to a battery of 4 V. the total
Resistance of the conductor is 4 Ω. Te net magnetic field at the centre of the conductor is
4V
(a) µ0
2
(b) 8µ0
3
(c) 2µ0
(d) zero
17. The magnetic field at P due to the magnet NS is
XP
900
O
N
S
(a) along OP
(b) along PO
(c) parallel to NS
(d) parallel to SN
18. A circular loop of mass m and radius r is lying in a horizontal (X-Y plane) table as shown in
figure. A uniform magnetic field B is applied parallel to x-axis. The current I in the loop, so that its
One edge just lifts from the table, is
I
0
X
R
(a) mg
πr2B
(c) mg
2πrB
(b) mg
πrB
(d) πrB
mgl
19. A conducting rod of length L and mass m is moving down a smooth inclined plane of inclination
Ѳ with constant speed v. A current I is flowing in the conductor perpendicular to the paper
inwards. A vertically upward magnetic field B exists in space there. The magnitude of magnetic field
B is
B
V
ѳ
Q
(a)
(b)
(c)
(d)
P
20. An electron moves in a circular orbit with a uniform speed v. it produces a magnetic field B at the
Centre of the circle. The radius of the circle is proportional to
(a)
(b)
(c)
v
(d)
B
B
v
21. A current of 1 A flows in a long straight wire. What is the magnetic field at a point 1 m away from
the wire?
(a) 200 MT
(b) 2 MT
(c) 0.2 × 10-6 T
(d) 2 × 10-7 T
22. Two circular coils of radii 10 cm and 40 cm are connected in series to a battery. The ratio of
Magnetic field at their centres is
(a) 1 : 4
(2) 4 : 1
(3) 2 : 1
(d) 1 : 2
23. A circular current carrying coil has a radius R. at what distance from the centre of coil on the
Axis when the magnetic induction will be of its value at centre of coil is
(a)
(b) R
(c) 2R
(d) 2R
24. In the above question, what is the equivalent dipole moment? (in A-m2)
(a) 8.9 × 10-24
(b) zero
(c) 9.7 × 10-3
(d) 10-24
25. Through two wires A and B, kept parallel to each other, 10 A and 2 A current are passed respectively
in opposite directions. If the wire A is infinitely long and the length of the wire B is 2 m, the force
in the conductor B which is situated at 10 cm distance from A will be
(a) 8 × 10-5 N
(b) 4 × 10-7 N
(c) 4 × 10-5 N
(d) 4π × 10-7 N
26. A wire, carrying a current I, is kept in the X-Y plane along the curve y = A sin (
x). a magnetic field B
exists in the z-direction. The magnetic of the magnetic force on the portion of the wire between
X =0 and x = λ is
(a) I λ B
(b)
iλB
(c) 2 I λB
(d) 3 I λB
27. The direction of force due to earth’s magnetic field on a wire carrying current vertically downward
Is
(a) horizontally towards east
(b) horizontally towards west
(c) horizontally towards north
(d) none of the above
28. The magnetic field inside a current carrying long wire of circular cross-section varies as (r = distance
From the centre)
(a) r0
(c) r2
(b) r
(d) r3
29. The acceleration of an electron at a certain moment in a magnetic field B =2î + 3Ĵ + 4Ќ is a =x î + Ĵ – Ќ
The value of x is
(a) 0.5
(b) 1
(c) 2.5
(d) 1.5
30. Two wire are placed at (2, 0. 0) and (-2, 0, 0) and are carrying equal currents along negative z-axis.
Magnetic field at point ( o, 2, 0) is along
(a) positive x-axis
(b) negative y-axis
(c) positive y-axis
(d) negative z-axis