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# Practice Test - Magnetic effects & Magnetism Notes | EduRev

Created by: Vikas Sharma

## : Practice Test - Magnetic effects & Magnetism Notes | EduRev

``` Page 1



Test -04_Magnetic effects & Magnetism
1. An iron rod of volume 10
-4
m
3
and relative
permeability 1000 is placed inside a long solenoid
wound with 5 turns/cm. If a current of 0.5 A is
passed through the solenoid, then the magnetic
moment of the rod is :
(a) 10 Am
2
(b) 15 Am
2

(c) 20 Am
2
(d) 25 Am
2

2. For substances hystersis (B-H) curves are given as
shown in figure. For making temporary magnet
which of the following is best :

3. The B-H curves (a) and (b) shown in the figure are
associated with :
(a) a diamagnetic and a
paramagnetic substance
respectively
(b) a paramagnetic and a
ferromagnetic substance
respectively
(c) soft iron and steel
respectively
(d) steel and soft iron respectively
4. SI unit for measuring magnetic flux is called :
(a) oersted  (b) maxwell
(c) weber  (d) gauss
5. The figure illustrate how B,
the flux density inside  a
sample of unmagnetised
ferromagnetic material
varies with B 0
the magnetic
flux density in which the
sample is kept. For the
sample to be suitable for making a permanent
magnet,
(a) OQ should be large, OR should be small
(b) OQ and OR should both be large
(c) OQ should be small and OR should be large
(d) OQ and OR should both be small
6. The variation of the intensity of magnetisation (I)
with respect to the magnetising field (H) in a
diamagnetic substance is described by the graph
(a) OD

(b) OC

(c) OB
(d) OA
7. In figure , the magnetic induction B at the center
O is
(a)
R 2
I
R 4
I
0 0
p
µ
-
µ
(inwards)
(b)
R 4
I
0
µ
(inwards)
(c)
R 8
I
0
µ
(inwards)
(d)
R 2
I
R 8
I
0 0
p
µ
+
µ
(inwards)
8. It is placed in a uniform
magnetic field
?
B ( out of paper)
such that its plane is
perpendicular to the direction
of
?
B . The wire will experience
(a) No force  (b) A stretching force
(c) A compressive force  (d) A torque
9. In the figure , shown the magnetic induction at
the centre of there are due to the current in will be

(a)
r
i
0
µ
(b)
r 2
i
0
µ

(c)
r 4
i
0
µ
(d) Zero
10. A rod of a paramagnetic substance is placed in a
non-uniform magnetic field. Which of the
following figure shows its alignment in the field :

Page 2



Test -04_Magnetic effects & Magnetism
1. An iron rod of volume 10
-4
m
3
and relative
permeability 1000 is placed inside a long solenoid
wound with 5 turns/cm. If a current of 0.5 A is
passed through the solenoid, then the magnetic
moment of the rod is :
(a) 10 Am
2
(b) 15 Am
2

(c) 20 Am
2
(d) 25 Am
2

2. For substances hystersis (B-H) curves are given as
shown in figure. For making temporary magnet
which of the following is best :

3. The B-H curves (a) and (b) shown in the figure are
associated with :
(a) a diamagnetic and a
paramagnetic substance
respectively
(b) a paramagnetic and a
ferromagnetic substance
respectively
(c) soft iron and steel
respectively
(d) steel and soft iron respectively
4. SI unit for measuring magnetic flux is called :
(a) oersted  (b) maxwell
(c) weber  (d) gauss
5. The figure illustrate how B,
the flux density inside  a
sample of unmagnetised
ferromagnetic material
varies with B 0
the magnetic
flux density in which the
sample is kept. For the
sample to be suitable for making a permanent
magnet,
(a) OQ should be large, OR should be small
(b) OQ and OR should both be large
(c) OQ should be small and OR should be large
(d) OQ and OR should both be small
6. The variation of the intensity of magnetisation (I)
with respect to the magnetising field (H) in a
diamagnetic substance is described by the graph
(a) OD

(b) OC

(c) OB
(d) OA
7. In figure , the magnetic induction B at the center
O is
(a)
R 2
I
R 4
I
0 0
p
µ
-
µ
(inwards)
(b)
R 4
I
0
µ
(inwards)
(c)
R 8
I
0
µ
(inwards)
(d)
R 2
I
R 8
I
0 0
p
µ
+
µ
(inwards)
8. It is placed in a uniform
magnetic field
?
B ( out of paper)
such that its plane is
perpendicular to the direction
of
?
B . The wire will experience
(a) No force  (b) A stretching force
(c) A compressive force  (d) A torque
9. In the figure , shown the magnetic induction at
the centre of there are due to the current in will be

(a)
r
i
0
µ
(b)
r 2
i
0
µ

(c)
r 4
i
0
µ
(d) Zero
10. A rod of a paramagnetic substance is placed in a
non-uniform magnetic field. Which of the
following figure shows its alignment in the field :



11. The variation of magnetic susceptibility ( ?) with
magnetizing field for a paramagnetic substance is

12. The ratio of magnetic moments of two short
magnets which gives null deflection in tan B
position at 12 cm and 18 cm from the centre of a
deflection magnetometer is :
(a) 2 : 3  (b) 8 : 27
(c) 27 : 8  (d) 4 : 9
13. The net magnetic
moment of two identical
magnets each of
magnetic moment M 0
,
inclined at 60 ° with each
other is :
(a) M
0

(b) 2 M
0

(c) 3 M
0

(d) 2M
0

14. The S.I. unit of magnetic dipole moment is
(a) AM
–1
(b) AM
2

(c) TMA
–1
(d) TMA
–2

15. Curie’s law can be written as
(a) ? ?(T–T
C
) (b) ? ?
C
T T
1
-

(c) ? ?
T
1
(d) ? ?T
16. In the above problem, if the straight wires are
turned upwards as shown in fig, then the value of
B at the centre O is given by
(a)
R 2
I
R 4
I
0 0
p
µ
-
µ
(inwards)
(b)
R 2
I
R 4
I
0 0
p
µ
-
µ
(outwards)
(c)
R 2
I
R 4
I
0 0
p
µ
+
µ
(outwards)
(d)
R 4
I
0
µ
(inwards)

17. A and B are two concentric circular conductors of
centre O and current I
1
and I
2

figure. It ratio of the flux
densities at O due to A and B
is 1 : 3, then the value of I
1
/I
2

is

(a)
6
1
(b)
4
1

(c)
3
1
(d)
2
1

18. A current i is flowing a loop of
radius r as shown in the figure.
The magnetic induction
intensity at the centre O will be

(a)
r 4
i
0
p
µ
? (b)
2
0
r 4
sin i 2
p
? µ

(c)
r 2
sin i 2
0
? µ
(d)
r 4
sin i
0
? µ

19. If f
1
and f
2
be the angles of dip observed in two
vertical planes at right angles to each other and f
be the true angle of dip, then :
(a) cos
2
f = cos
2
f
1
+ cos
2
f
2

(b) sec f = sec
2
f
1
+ sec
2
f
2

(c) tan
2
f = tan
2
f
1
+ tan
2
f
2

(d) cot
2
f = cot
2
f
1
+ cot
2
f
2

20. A rod of a diamagnetic material is placed in a
non-uniform strong magnetic field. Which of the
figure below shows the alignment of the rod in
the field :

21. If the symbols have their usual meanings, the
expression
MH
I
has the dimensions of :
(a) frequency  (b) time
(c) distance  (d) None of these

22. Which of the following is most suitable for the
core of the electromagnets  :
(a) Air  (b) Steel
(c) Soft iron  (d) Cu-Ni alloy
Page 3



Test -04_Magnetic effects & Magnetism
1. An iron rod of volume 10
-4
m
3
and relative
permeability 1000 is placed inside a long solenoid
wound with 5 turns/cm. If a current of 0.5 A is
passed through the solenoid, then the magnetic
moment of the rod is :
(a) 10 Am
2
(b) 15 Am
2

(c) 20 Am
2
(d) 25 Am
2

2. For substances hystersis (B-H) curves are given as
shown in figure. For making temporary magnet
which of the following is best :

3. The B-H curves (a) and (b) shown in the figure are
associated with :
(a) a diamagnetic and a
paramagnetic substance
respectively
(b) a paramagnetic and a
ferromagnetic substance
respectively
(c) soft iron and steel
respectively
(d) steel and soft iron respectively
4. SI unit for measuring magnetic flux is called :
(a) oersted  (b) maxwell
(c) weber  (d) gauss
5. The figure illustrate how B,
the flux density inside  a
sample of unmagnetised
ferromagnetic material
varies with B 0
the magnetic
flux density in which the
sample is kept. For the
sample to be suitable for making a permanent
magnet,
(a) OQ should be large, OR should be small
(b) OQ and OR should both be large
(c) OQ should be small and OR should be large
(d) OQ and OR should both be small
6. The variation of the intensity of magnetisation (I)
with respect to the magnetising field (H) in a
diamagnetic substance is described by the graph
(a) OD

(b) OC

(c) OB
(d) OA
7. In figure , the magnetic induction B at the center
O is
(a)
R 2
I
R 4
I
0 0
p
µ
-
µ
(inwards)
(b)
R 4
I
0
µ
(inwards)
(c)
R 8
I
0
µ
(inwards)
(d)
R 2
I
R 8
I
0 0
p
µ
+
µ
(inwards)
8. It is placed in a uniform
magnetic field
?
B ( out of paper)
such that its plane is
perpendicular to the direction
of
?
B . The wire will experience
(a) No force  (b) A stretching force
(c) A compressive force  (d) A torque
9. In the figure , shown the magnetic induction at
the centre of there are due to the current in will be

(a)
r
i
0
µ
(b)
r 2
i
0
µ

(c)
r 4
i
0
µ
(d) Zero
10. A rod of a paramagnetic substance is placed in a
non-uniform magnetic field. Which of the
following figure shows its alignment in the field :



11. The variation of magnetic susceptibility ( ?) with
magnetizing field for a paramagnetic substance is

12. The ratio of magnetic moments of two short
magnets which gives null deflection in tan B
position at 12 cm and 18 cm from the centre of a
deflection magnetometer is :
(a) 2 : 3  (b) 8 : 27
(c) 27 : 8  (d) 4 : 9
13. The net magnetic
moment of two identical
magnets each of
magnetic moment M 0
,
inclined at 60 ° with each
other is :
(a) M
0

(b) 2 M
0

(c) 3 M
0

(d) 2M
0

14. The S.I. unit of magnetic dipole moment is
(a) AM
–1
(b) AM
2

(c) TMA
–1
(d) TMA
–2

15. Curie’s law can be written as
(a) ? ?(T–T
C
) (b) ? ?
C
T T
1
-

(c) ? ?
T
1
(d) ? ?T
16. In the above problem, if the straight wires are
turned upwards as shown in fig, then the value of
B at the centre O is given by
(a)
R 2
I
R 4
I
0 0
p
µ
-
µ
(inwards)
(b)
R 2
I
R 4
I
0 0
p
µ
-
µ
(outwards)
(c)
R 2
I
R 4
I
0 0
p
µ
+
µ
(outwards)
(d)
R 4
I
0
µ
(inwards)

17. A and B are two concentric circular conductors of
centre O and current I
1
and I
2

figure. It ratio of the flux
densities at O due to A and B
is 1 : 3, then the value of I
1
/I
2

is

(a)
6
1
(b)
4
1

(c)
3
1
(d)
2
1

18. A current i is flowing a loop of
radius r as shown in the figure.
The magnetic induction
intensity at the centre O will be

(a)
r 4
i
0
p
µ
? (b)
2
0
r 4
sin i 2
p
? µ

(c)
r 2
sin i 2
0
? µ
(d)
r 4
sin i
0
? µ

19. If f
1
and f
2
be the angles of dip observed in two
vertical planes at right angles to each other and f
be the true angle of dip, then :
(a) cos
2
f = cos
2
f
1
+ cos
2
f
2

(b) sec f = sec
2
f
1
+ sec
2
f
2

(c) tan
2
f = tan
2
f
1
+ tan
2
f
2

(d) cot
2
f = cot
2
f
1
+ cot
2
f
2

20. A rod of a diamagnetic material is placed in a
non-uniform strong magnetic field. Which of the
figure below shows the alignment of the rod in
the field :

21. If the symbols have their usual meanings, the
expression
MH
I
has the dimensions of :
(a) frequency  (b) time
(c) distance  (d) None of these

22. Which of the following is most suitable for the
core of the electromagnets  :
(a) Air  (b) Steel
(c) Soft iron  (d) Cu-Ni alloy


23. The ratio of SI unit to C.G.S. unit for magnetic flux
density is :
(a) 10
3
(b) 10
4

(c) 10
-4
(d) 10
-3

24. Identify the paramagnetic substance
(a) Iron  (b) Aluminium
(c) Nickel  (d) Hydrogen
25. A frog can be deviated in a magnetic field
produced by a current in a vertical solenoid
placed below the frog. This is possible because the
body of the frog behaves as
(a) Paramagnetic
(b) Diamagnetic
(c) Ferromagnetic
(d) Antiferromagnetic
In every question a statement of ASSERTION is
followed by a statement of REASON. Mark the
correct answer out of the following choices:
(a) If both ASSERTION and REASON are true
and reason is the correct explanation of the
assertion.
(b) If both ASSERTION and REASON are true
but reason is not the correct explanation of the
assertion.
(c) If ASSERTION is true but REASON is false.
(d) If ASSERTION is false but REASON is true.
26. Assertion: When a magnet of length L and
magnetic moment M is bent to form a
semicircular arc, the new magnetic moment is
2M/ p.
Reason: Magnetic moment of a magnet depends
only upon the distance between the poles of the
magnet.
27. Assertion: An iron nail placed in the magnetic
field of a bar magnet experiences a torque as well
as a force.
Reason: The magnetic field near a bar magnet is
non-uniform
28. Assertion: Ferromagnetic substances do not obey
Curies law.
Reason:  Above the Curie temperature, a
ferromagnetic substance shows paramagnetic
properties.
29. Assertion: Copper is diamagnetic but copper
chloride is attracted by magnetic fields.
Reason: Copper chloride is paramagnetic.
30. Assertion: A liquid contained in one limb of a
narrow U-tube is placed between the pole pieces
of an electromagnet, with the meniscus in line
with the field as shown. On switching on the
electromagnet the level in the limb goes up
slightly.

Reason: The liquid is paramagnetic.

1 d 6 B 11 A 16 D 21 B 26 C
2 d 7 C 12 B 17 A                                                                                                                                                                                              22 C 27 A
3 C 8 B 13 C 18 A 23 B 28 B
4 C 9 C 14 B 19 D 24 D 29 A
5 B 10 A 15
C
20 D 25 B 30 A

SOLUTIONS
1. Use M= NIA
2. For a temporary  magnet the hystersis loop  should  be long and narrow.
3. (c)
4. 1 Wb = 1 Tm
2

5. In the given figure OQ refers to retentivity while OR refers to corecivity should be high.
6. Intensity of magnetization of diamagnetic substance is very small and negative.
Page 4



Test -04_Magnetic effects & Magnetism
1. An iron rod of volume 10
-4
m
3
and relative
permeability 1000 is placed inside a long solenoid
wound with 5 turns/cm. If a current of 0.5 A is
passed through the solenoid, then the magnetic
moment of the rod is :
(a) 10 Am
2
(b) 15 Am
2

(c) 20 Am
2
(d) 25 Am
2

2. For substances hystersis (B-H) curves are given as
shown in figure. For making temporary magnet
which of the following is best :

3. The B-H curves (a) and (b) shown in the figure are
associated with :
(a) a diamagnetic and a
paramagnetic substance
respectively
(b) a paramagnetic and a
ferromagnetic substance
respectively
(c) soft iron and steel
respectively
(d) steel and soft iron respectively
4. SI unit for measuring magnetic flux is called :
(a) oersted  (b) maxwell
(c) weber  (d) gauss
5. The figure illustrate how B,
the flux density inside  a
sample of unmagnetised
ferromagnetic material
varies with B 0
the magnetic
flux density in which the
sample is kept. For the
sample to be suitable for making a permanent
magnet,
(a) OQ should be large, OR should be small
(b) OQ and OR should both be large
(c) OQ should be small and OR should be large
(d) OQ and OR should both be small
6. The variation of the intensity of magnetisation (I)
with respect to the magnetising field (H) in a
diamagnetic substance is described by the graph
(a) OD

(b) OC

(c) OB
(d) OA
7. In figure , the magnetic induction B at the center
O is
(a)
R 2
I
R 4
I
0 0
p
µ
-
µ
(inwards)
(b)
R 4
I
0
µ
(inwards)
(c)
R 8
I
0
µ
(inwards)
(d)
R 2
I
R 8
I
0 0
p
µ
+
µ
(inwards)
8. It is placed in a uniform
magnetic field
?
B ( out of paper)
such that its plane is
perpendicular to the direction
of
?
B . The wire will experience
(a) No force  (b) A stretching force
(c) A compressive force  (d) A torque
9. In the figure , shown the magnetic induction at
the centre of there are due to the current in will be

(a)
r
i
0
µ
(b)
r 2
i
0
µ

(c)
r 4
i
0
µ
(d) Zero
10. A rod of a paramagnetic substance is placed in a
non-uniform magnetic field. Which of the
following figure shows its alignment in the field :



11. The variation of magnetic susceptibility ( ?) with
magnetizing field for a paramagnetic substance is

12. The ratio of magnetic moments of two short
magnets which gives null deflection in tan B
position at 12 cm and 18 cm from the centre of a
deflection magnetometer is :
(a) 2 : 3  (b) 8 : 27
(c) 27 : 8  (d) 4 : 9
13. The net magnetic
moment of two identical
magnets each of
magnetic moment M 0
,
inclined at 60 ° with each
other is :
(a) M
0

(b) 2 M
0

(c) 3 M
0

(d) 2M
0

14. The S.I. unit of magnetic dipole moment is
(a) AM
–1
(b) AM
2

(c) TMA
–1
(d) TMA
–2

15. Curie’s law can be written as
(a) ? ?(T–T
C
) (b) ? ?
C
T T
1
-

(c) ? ?
T
1
(d) ? ?T
16. In the above problem, if the straight wires are
turned upwards as shown in fig, then the value of
B at the centre O is given by
(a)
R 2
I
R 4
I
0 0
p
µ
-
µ
(inwards)
(b)
R 2
I
R 4
I
0 0
p
µ
-
µ
(outwards)
(c)
R 2
I
R 4
I
0 0
p
µ
+
µ
(outwards)
(d)
R 4
I
0
µ
(inwards)

17. A and B are two concentric circular conductors of
centre O and current I
1
and I
2

figure. It ratio of the flux
densities at O due to A and B
is 1 : 3, then the value of I
1
/I
2

is

(a)
6
1
(b)
4
1

(c)
3
1
(d)
2
1

18. A current i is flowing a loop of
radius r as shown in the figure.
The magnetic induction
intensity at the centre O will be

(a)
r 4
i
0
p
µ
? (b)
2
0
r 4
sin i 2
p
? µ

(c)
r 2
sin i 2
0
? µ
(d)
r 4
sin i
0
? µ

19. If f
1
and f
2
be the angles of dip observed in two
vertical planes at right angles to each other and f
be the true angle of dip, then :
(a) cos
2
f = cos
2
f
1
+ cos
2
f
2

(b) sec f = sec
2
f
1
+ sec
2
f
2

(c) tan
2
f = tan
2
f
1
+ tan
2
f
2

(d) cot
2
f = cot
2
f
1
+ cot
2
f
2

20. A rod of a diamagnetic material is placed in a
non-uniform strong magnetic field. Which of the
figure below shows the alignment of the rod in
the field :

21. If the symbols have their usual meanings, the
expression
MH
I
has the dimensions of :
(a) frequency  (b) time
(c) distance  (d) None of these

22. Which of the following is most suitable for the
core of the electromagnets  :
(a) Air  (b) Steel
(c) Soft iron  (d) Cu-Ni alloy


23. The ratio of SI unit to C.G.S. unit for magnetic flux
density is :
(a) 10
3
(b) 10
4

(c) 10
-4
(d) 10
-3

24. Identify the paramagnetic substance
(a) Iron  (b) Aluminium
(c) Nickel  (d) Hydrogen
25. A frog can be deviated in a magnetic field
produced by a current in a vertical solenoid
placed below the frog. This is possible because the
body of the frog behaves as
(a) Paramagnetic
(b) Diamagnetic
(c) Ferromagnetic
(d) Antiferromagnetic
In every question a statement of ASSERTION is
followed by a statement of REASON. Mark the
correct answer out of the following choices:
(a) If both ASSERTION and REASON are true
and reason is the correct explanation of the
assertion.
(b) If both ASSERTION and REASON are true
but reason is not the correct explanation of the
assertion.
(c) If ASSERTION is true but REASON is false.
(d) If ASSERTION is false but REASON is true.
26. Assertion: When a magnet of length L and
magnetic moment M is bent to form a
semicircular arc, the new magnetic moment is
2M/ p.
Reason: Magnetic moment of a magnet depends
only upon the distance between the poles of the
magnet.
27. Assertion: An iron nail placed in the magnetic
field of a bar magnet experiences a torque as well
as a force.
Reason: The magnetic field near a bar magnet is
non-uniform
28. Assertion: Ferromagnetic substances do not obey
Curies law.
Reason:  Above the Curie temperature, a
ferromagnetic substance shows paramagnetic
properties.
29. Assertion: Copper is diamagnetic but copper
chloride is attracted by magnetic fields.
Reason: Copper chloride is paramagnetic.
30. Assertion: A liquid contained in one limb of a
narrow U-tube is placed between the pole pieces
of an electromagnet, with the meniscus in line
with the field as shown. On switching on the
electromagnet the level in the limb goes up
slightly.

Reason: The liquid is paramagnetic.

1 d 6 B 11 A 16 D 21 B 26 C
2 d 7 C 12 B 17 A                                                                                                                                                                                              22 C 27 A
3 C 8 B 13 C 18 A 23 B 28 B
4 C 9 C 14 B 19 D 24 D 29 A
5 B 10 A 15
C
20 D 25 B 30 A

SOLUTIONS
1. Use M= NIA
2. For a temporary  magnet the hystersis loop  should  be long and narrow.
3. (c)
4. 1 Wb = 1 Tm
2

5. In the given figure OQ refers to retentivity while OR refers to corecivity should be high.
6. Intensity of magnetization of diamagnetic substance is very small and negative.


7.
?
?
?
?
?
?
? µ
0
0
36 r 2
I
=
?
?
?
?
?
?
µ
0
0
36
90
r 2
I
=
r 8
I
0
µ

8. (B)
9. (C)
10. When a paramagnetic substance is placed in a non- uniform magnetic field, then substance always aligns
along the filed lines, because by aligning along the lines  of induction, magnetization is maximum
11. Susceptibility of a paramagnetic substance is independent  of magnetizing field.
12.
3
2
2
3
1
1
d
M
d
M
=   ?
27
8
3
2
d
d
M
M
3
3
2
1
2
1
=
?
?
?
?
?
?
=
?
?
?
?
?
?
?
?
=
13. (c)
14. (B)
15. (C)
16. The contribution of semi -circular wire is
R 4
I
0
µ
The two semi -infinite wires become one completely infinite
wire, thus the contribution of straight wires is
R 4
I
0
p
µ
The direction of B is inwards ?. Hence, B =
R 2
I
R 4
I
0 0
p
µ
-
µ

17. r
1
: r
2
= 1 : 2 and B
1
: B
2
= 1 : 3  We know that  B =
r 2
ni
0
µ
?
6
1
2 3
1 1
r B
r B
i
i
2 2
1 1
2
1
=
×
×
= =
18. In this case, 2 p = ?  Hence, from the formula B =
r
pi 2
.
4
0
p
µ
we get  B =
r
i
.
4
0
?
p
µ

19. Let a  be the angle which one of the planes make  with the magnetic meridian the other plane  makes  an angle
(90
o
– a) with it. The component of H in these planes will  be H cos a and H sin a  respectively. If f
1
and f
2
are
the apparent dips in these two planes, then
tan f
1
=
a cos H
V
i.e  cos a =
1
tan H
V
f
….(i)  tan f
2
=
a sin H
V

i.e sin a  =
2
tan H
V
f
….(ii)  Squaring and adding  equation (i) and (ii), we get
cos
2
a + sin
2
a =
2
H
V
?
?
?
?
?
?

?
?
?
?
?
?
?
?
f
=
f
2
2 2
tan
1
tan
1
i.e. 1 = ) cot (cot
H
V
2
2
1
2
2
2
f + f or
2
2
1
2
2
2
cot cot
V
H
f + f = i.e. cot
2

cot
2
f = cot
2
f
1
+ cot
2
f
2
This  is the required  result.
20. When a diamagnetic substance is placed in a non -uniform strong magnetic field, it always aligns itself
perpendicular to the lines of induction, hence repulsion. Magnetisation, hence susceptibility is negative.
21. (B)
22. Soft iron has highest susceptibility.
23. Magnetic flux density is the magnetic field.   1 T = 10
4
G  ?
4
10
G 1
T 1
=
24. (D)
25. Diamagnetic substance are repelled by the magnetic field.
26. (c) Assertion is true but reason is false
Consider a magnet of length L and pole strength m. Its magnetic moment = mL
Next bend it into a semicircular are of radius R.
Then R =
p
L
and the magnetic moment M
1
= m 2 R = .
M 2 L m 2
p
=
p

The assertion is true. The magnetic moment which depends upon the pole strength and the distance between
the poles is calculated as
p
M 2
. The reason is false. It is not only the distance between the poles but also the
pole strength which determines the magnetic moment.
27. (a) The reason is the correct explanation of the assertion and both are correct.
Any magnet placed in a non-uniform magnetic field experiences both a net force as well as a torque. The
magnetic field around a bar magnet is non-uniform. An iron nail placed in a magnetic field acquires induced
90
o
– a
H
1
= H cos a
H
H
2
= H sin a
Page 5



Test -04_Magnetic effects & Magnetism
1. An iron rod of volume 10
-4
m
3
and relative
permeability 1000 is placed inside a long solenoid
wound with 5 turns/cm. If a current of 0.5 A is
passed through the solenoid, then the magnetic
moment of the rod is :
(a) 10 Am
2
(b) 15 Am
2

(c) 20 Am
2
(d) 25 Am
2

2. For substances hystersis (B-H) curves are given as
shown in figure. For making temporary magnet
which of the following is best :

3. The B-H curves (a) and (b) shown in the figure are
associated with :
(a) a diamagnetic and a
paramagnetic substance
respectively
(b) a paramagnetic and a
ferromagnetic substance
respectively
(c) soft iron and steel
respectively
(d) steel and soft iron respectively
4. SI unit for measuring magnetic flux is called :
(a) oersted  (b) maxwell
(c) weber  (d) gauss
5. The figure illustrate how B,
the flux density inside  a
sample of unmagnetised
ferromagnetic material
varies with B 0
the magnetic
flux density in which the
sample is kept. For the
sample to be suitable for making a permanent
magnet,
(a) OQ should be large, OR should be small
(b) OQ and OR should both be large
(c) OQ should be small and OR should be large
(d) OQ and OR should both be small
6. The variation of the intensity of magnetisation (I)
with respect to the magnetising field (H) in a
diamagnetic substance is described by the graph
(a) OD

(b) OC

(c) OB
(d) OA
7. In figure , the magnetic induction B at the center
O is
(a)
R 2
I
R 4
I
0 0
p
µ
-
µ
(inwards)
(b)
R 4
I
0
µ
(inwards)
(c)
R 8
I
0
µ
(inwards)
(d)
R 2
I
R 8
I
0 0
p
µ
+
µ
(inwards)
8. It is placed in a uniform
magnetic field
?
B ( out of paper)
such that its plane is
perpendicular to the direction
of
?
B . The wire will experience
(a) No force  (b) A stretching force
(c) A compressive force  (d) A torque
9. In the figure , shown the magnetic induction at
the centre of there are due to the current in will be

(a)
r
i
0
µ
(b)
r 2
i
0
µ

(c)
r 4
i
0
µ
(d) Zero
10. A rod of a paramagnetic substance is placed in a
non-uniform magnetic field. Which of the
following figure shows its alignment in the field :



11. The variation of magnetic susceptibility ( ?) with
magnetizing field for a paramagnetic substance is

12. The ratio of magnetic moments of two short
magnets which gives null deflection in tan B
position at 12 cm and 18 cm from the centre of a
deflection magnetometer is :
(a) 2 : 3  (b) 8 : 27
(c) 27 : 8  (d) 4 : 9
13. The net magnetic
moment of two identical
magnets each of
magnetic moment M 0
,
inclined at 60 ° with each
other is :
(a) M
0

(b) 2 M
0

(c) 3 M
0

(d) 2M
0

14. The S.I. unit of magnetic dipole moment is
(a) AM
–1
(b) AM
2

(c) TMA
–1
(d) TMA
–2

15. Curie’s law can be written as
(a) ? ?(T–T
C
) (b) ? ?
C
T T
1
-

(c) ? ?
T
1
(d) ? ?T
16. In the above problem, if the straight wires are
turned upwards as shown in fig, then the value of
B at the centre O is given by
(a)
R 2
I
R 4
I
0 0
p
µ
-
µ
(inwards)
(b)
R 2
I
R 4
I
0 0
p
µ
-
µ
(outwards)
(c)
R 2
I
R 4
I
0 0
p
µ
+
µ
(outwards)
(d)
R 4
I
0
µ
(inwards)

17. A and B are two concentric circular conductors of
centre O and current I
1
and I
2

figure. It ratio of the flux
densities at O due to A and B
is 1 : 3, then the value of I
1
/I
2

is

(a)
6
1
(b)
4
1

(c)
3
1
(d)
2
1

18. A current i is flowing a loop of
radius r as shown in the figure.
The magnetic induction
intensity at the centre O will be

(a)
r 4
i
0
p
µ
? (b)
2
0
r 4
sin i 2
p
? µ

(c)
r 2
sin i 2
0
? µ
(d)
r 4
sin i
0
? µ

19. If f
1
and f
2
be the angles of dip observed in two
vertical planes at right angles to each other and f
be the true angle of dip, then :
(a) cos
2
f = cos
2
f
1
+ cos
2
f
2

(b) sec f = sec
2
f
1
+ sec
2
f
2

(c) tan
2
f = tan
2
f
1
+ tan
2
f
2

(d) cot
2
f = cot
2
f
1
+ cot
2
f
2

20. A rod of a diamagnetic material is placed in a
non-uniform strong magnetic field. Which of the
figure below shows the alignment of the rod in
the field :

21. If the symbols have their usual meanings, the
expression
MH
I
has the dimensions of :
(a) frequency  (b) time
(c) distance  (d) None of these

22. Which of the following is most suitable for the
core of the electromagnets  :
(a) Air  (b) Steel
(c) Soft iron  (d) Cu-Ni alloy


23. The ratio of SI unit to C.G.S. unit for magnetic flux
density is :
(a) 10
3
(b) 10
4

(c) 10
-4
(d) 10
-3

24. Identify the paramagnetic substance
(a) Iron  (b) Aluminium
(c) Nickel  (d) Hydrogen
25. A frog can be deviated in a magnetic field
produced by a current in a vertical solenoid
placed below the frog. This is possible because the
body of the frog behaves as
(a) Paramagnetic
(b) Diamagnetic
(c) Ferromagnetic
(d) Antiferromagnetic
In every question a statement of ASSERTION is
followed by a statement of REASON. Mark the
correct answer out of the following choices:
(a) If both ASSERTION and REASON are true
and reason is the correct explanation of the
assertion.
(b) If both ASSERTION and REASON are true
but reason is not the correct explanation of the
assertion.
(c) If ASSERTION is true but REASON is false.
(d) If ASSERTION is false but REASON is true.
26. Assertion: When a magnet of length L and
magnetic moment M is bent to form a
semicircular arc, the new magnetic moment is
2M/ p.
Reason: Magnetic moment of a magnet depends
only upon the distance between the poles of the
magnet.
27. Assertion: An iron nail placed in the magnetic
field of a bar magnet experiences a torque as well
as a force.
Reason: The magnetic field near a bar magnet is
non-uniform
28. Assertion: Ferromagnetic substances do not obey
Curies law.
Reason:  Above the Curie temperature, a
ferromagnetic substance shows paramagnetic
properties.
29. Assertion: Copper is diamagnetic but copper
chloride is attracted by magnetic fields.
Reason: Copper chloride is paramagnetic.
30. Assertion: A liquid contained in one limb of a
narrow U-tube is placed between the pole pieces
of an electromagnet, with the meniscus in line
with the field as shown. On switching on the
electromagnet the level in the limb goes up
slightly.

Reason: The liquid is paramagnetic.

1 d 6 B 11 A 16 D 21 B 26 C
2 d 7 C 12 B 17 A                                                                                                                                                                                              22 C 27 A
3 C 8 B 13 C 18 A 23 B 28 B
4 C 9 C 14 B 19 D 24 D 29 A
5 B 10 A 15
C
20 D 25 B 30 A

SOLUTIONS
1. Use M= NIA
2. For a temporary  magnet the hystersis loop  should  be long and narrow.
3. (c)
4. 1 Wb = 1 Tm
2

5. In the given figure OQ refers to retentivity while OR refers to corecivity should be high.
6. Intensity of magnetization of diamagnetic substance is very small and negative.


7.
?
?
?
?
?
?
? µ
0
0
36 r 2
I
=
?
?
?
?
?
?
µ
0
0
36
90
r 2
I
=
r 8
I
0
µ

8. (B)
9. (C)
10. When a paramagnetic substance is placed in a non- uniform magnetic field, then substance always aligns
along the filed lines, because by aligning along the lines  of induction, magnetization is maximum
11. Susceptibility of a paramagnetic substance is independent  of magnetizing field.
12.
3
2
2
3
1
1
d
M
d
M
=   ?
27
8
3
2
d
d
M
M
3
3
2
1
2
1
=
?
?
?
?
?
?
=
?
?
?
?
?
?
?
?
=
13. (c)
14. (B)
15. (C)
16. The contribution of semi -circular wire is
R 4
I
0
µ
The two semi -infinite wires become one completely infinite
wire, thus the contribution of straight wires is
R 4
I
0
p
µ
The direction of B is inwards ?. Hence, B =
R 2
I
R 4
I
0 0
p
µ
-
µ

17. r
1
: r
2
= 1 : 2 and B
1
: B
2
= 1 : 3  We know that  B =
r 2
ni
0
µ
?
6
1
2 3
1 1
r B
r B
i
i
2 2
1 1
2
1
=
×
×
= =
18. In this case, 2 p = ?  Hence, from the formula B =
r
pi 2
.
4
0
p
µ
we get  B =
r
i
.
4
0
?
p
µ

19. Let a  be the angle which one of the planes make  with the magnetic meridian the other plane  makes  an angle
(90
o
– a) with it. The component of H in these planes will  be H cos a and H sin a  respectively. If f
1
and f
2
are
the apparent dips in these two planes, then
tan f
1
=
a cos H
V
i.e  cos a =
1
tan H
V
f
….(i)  tan f
2
=
a sin H
V

i.e sin a  =
2
tan H
V
f
….(ii)  Squaring and adding  equation (i) and (ii), we get
cos
2
a + sin
2
a =
2
H
V
?
?
?
?
?
?

?
?
?
?
?
?
?
?
f
=
f
2
2 2
tan
1
tan
1
i.e. 1 = ) cot (cot
H
V
2
2
1
2
2
2
f + f or
2
2
1
2
2
2
cot cot
V
H
f + f = i.e. cot
2

cot
2
f = cot
2
f
1
+ cot
2
f
2
This  is the required  result.
20. When a diamagnetic substance is placed in a non -uniform strong magnetic field, it always aligns itself
perpendicular to the lines of induction, hence repulsion. Magnetisation, hence susceptibility is negative.
21. (B)
22. Soft iron has highest susceptibility.
23. Magnetic flux density is the magnetic field.   1 T = 10
4
G  ?
4
10
G 1
T 1
=
24. (D)
25. Diamagnetic substance are repelled by the magnetic field.
26. (c) Assertion is true but reason is false
Consider a magnet of length L and pole strength m. Its magnetic moment = mL
Next bend it into a semicircular are of radius R.
Then R =
p
L
and the magnetic moment M
1
= m 2 R = .
M 2 L m 2
p
=
p

The assertion is true. The magnetic moment which depends upon the pole strength and the distance between
the poles is calculated as
p
M 2
. The reason is false. It is not only the distance between the poles but also the
pole strength which determines the magnetic moment.
27. (a) The reason is the correct explanation of the assertion and both are correct.
Any magnet placed in a non-uniform magnetic field experiences both a net force as well as a torque. The
magnetic field around a bar magnet is non-uniform. An iron nail placed in a magnetic field acquires induced
90
o
– a
H
1
= H cos a
H
H
2
= H sin a


magnetization. Thus the iron nail experiences a torque as well as a force when placed in the non-uniform
magnetic field of a bar magnet.
28. (b) Both the assertion and reason are correct independent statements.
Till a certain temperature the susceptibility of ferromagnetic substances do not follow the variation given by
Curie’s law. At a critical temperature called Curie’s temperature the material loses its ferromagnetic properties
and becomes paramagnetic. Above this temperature the variation of susceptibility is according to Curie’s law.
29. (a) The reason is true. It explains the assertion which is also true.
Copper is diamagnetic. It is not necessary that all compounds or alloys of copper will also be diamagnetic. As
copper chloride is paramagnetic it will be attracted by strong magnetic fields.
30. (a) The reason is true. It explains the assertion which is also true.
Both paramagnetic and ferromagnetic substances are attracted by magnetic fields. However, the force of
attraction is weak for paramagnetic substances and very strong for ferromagnetic substances. When the
electromagnet is switched ON, the magnetic field attracts more of the liquid and the level rises. For a
paramagnetic liquid, the force being less the level rises only by a slight amount. The assertion is correct based
on the information in the reason.

```