The relation between $B,H{\rm{\;and}}\;I$ in SI unit is

$B = {{\rm{\mu }}_0}\left( {H + I} \right)$

$H = $${{\rm{\mu }}_0}\left( {B + I} \right)$

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NEET • PHYSICS • MAGNETISM AND MATTER

Magnetism and matter practice · Medium

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Showing 1-30 of 128 questions

1 Medium

1 of 128

Application +4 | -1

The area of hysteresis loop of a material is equivalent to

250\;joule

. When

10\;kg

material is magnetized by an alternating field of

50\;Hz

then energy lost in one hour will be (density of material is

7.5\;gm/c{m^3}

)

View answer and explanation

Correct option: A

6 \times {10^4}J

Option A is correct. The energy lost per unit volume per cycle is given, and the total energy loss is calculated based on the volume and frequency.

2 Medium

2 of 128

Analyzing +4 | -1

Assertion(A): Earth's magnetic field inside a closed iron box is less as compared to the out side.

Reason(R): The magnetic permeability of iron is low.

View answer and explanation

Correct option: C

If (A) is true but the (R) is false

Option C (If (A) is true but the (R) is false) is correct because the magnetic field inside a closed iron box is less due to the high permeability of iron, not low permeability.

3 Medium

3 of 128

Application +4 | -1

Force between two identical short bar magnets whose centers are

r

metre apart is 8.1 N, when their axes are along the same line. If separation is increased to 3

r

and the axis are rearranged perpendicularly, the force between them would become

View answer and explanation

Correct option: C

0.1 N

Option C (0.1 N) is correct because the force between the magnets changes with distance and orientation.

4 Medium

4 of 128

Understanding +4 | -1

The vertical component of earth’s magnetic field is zero or The earth’s magnetic field always has a vertical component except at the

View answer and explanation

Correct option: D

Magnetic equator

Option D (Magnetic equator) is correct because the vertical component of the Earth's magnetic field is zero at the magnetic equator.

5 Medium

5 of 128

Remembering +4 | -1

The magnetising field required to be applied in opposite direction to reduce residual magnetism to zero is called

View answer and explanation

Correct option: A

Coercivity

Option A (Coercivity) is correct because coercivity is the measure of the magnetic field required to reduce the residual magnetism of a material to zero.

6 Medium

6 of 128

Understanding +4 | -1

At the magnetic poles of the earth, a compass needle will be

View answer and explanation

Correct option: B

Bent slightly

Option A (Vertical) is correct because at the magnetic poles, the Earth's magnetic field lines are nearly vertical, causing the compass needle to point almost vertically downwards or upwards.

7 Medium

7 of 128

Understanding +4 | -1

At a point on the right bisector of a magnetic dipole magnetic

View answer and explanation

Correct option: A

Potential varies as

\frac{1}{{{r^2}}}

Option B is correct. The magnetic potential is zero at all points on the right bisector of a magnetic dipole.

8 Medium

8 of 128

Understanding +4 | -1

A dip needle which is free to move in a vertical plane perpendicular to magnetic meridian will remain

View answer and explanation

Correct option: B

Vertical

Option B (Vertical) is correct because a dip needle free to move in a vertical plane perpendicular to the magnetic meridian will align itself with the vertical component of the Earth's magnetic field.

9 Medium

9 of 128

Remembering +4 | -1

The ultimate individual unit of magnetism is any magnet is called

View answer and explanation

Correct option: C

Dipole

Option C is correct. The ultimate individual unit of magnetism is a dipole, as single magnetic poles (monopoles) have not been observed.

10 Medium

10 of 128

Understanding +4 | -1

A magnetic needle is placed with its north pole
facing north in north south direction. In its
map of magnetic field the null point will be

View answer and explanation

Correct option: A

on its equatorial line

Option A (on its equatorial line) is correct because when a magnetic needle is aligned with the Earth's field, the null points are on the equatorial line.

11 Medium

11 of 128

Application +4 | -1

If two identical bar magnets, each of length

l,

pole strength

m

and magnet moment

M,

are placed perpendicular to each other with their unlike poles in contact, the magnetic moment of the combination is

View answer and explanation

Correct option: B

lm\left( {\sqrt 2 } \right)

Option B (

lm\left( {\sqrt 2 } \right)

) is correct because the magnetic moments add vectorially, resulting in a net magnetic moment of

\sqrt{M^2 + M^2} = M\sqrt{2} = lm\sqrt{2}

12 Medium

12 of 128

Understanding +4 | -1

A magnet of magnetic moment

M

is freely suspended in a uniform magnetic field strength B. The work done is deflecting the magnet through an angle

\theta

is given by

View answer and explanation

Correct option: D

\mathrm{MB}(1-\cos \theta)

Option D is correct because the work done in deflecting a magnet in a magnetic field is given by MB(1-cosθ), which represents the change in potential energy.

13 Medium

13 of 128

Remembering +4 | -1

Substances in which the magnetic moment of a single atom is not zero, is known as

View answer and explanation

Correct option: C

Paramagnetism

Option C (Paramagnetism) is correct because paramagnetic substances have atoms with non-zero magnetic moments that align weakly with an external field.

14 Medium

14 of 128

Application +4 | -1

A bar magnet of magnetic moment 3.0 A-

{m^2}

is placed in a uniform magnetic induction field of

2 \times {10^{ - 5}}T

. If each pole of the magnet experiences a force of

6 \times {10^{ - 4}}N

, the length of the magnet is

View answer and explanation

Correct option: D

0.1

m

Option D is correct because the length of the magnet is calculated using the formula relating force, magnetic moment, and magnetic field, resulting in 0.1 m.

15 Medium

15 of 128

Understanding +4 | -1

A bar magnet is suspended from the middle
point in a uniform magnetic field. The couple
acting on the bar magnet is minimum when the
magnet is

View answer and explanation

Correct option: A

parallel to the field

Option A (parallel to the field) is correct because the torque on a magnet is minimum when it's aligned with the magnetic field.

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16 Medium

16 of 128

Understanding +4 | -1

The intensity of magnetic field is

H

and moment of magnet is

M

. The maximum potential energy is

View answer and explanation

Correct option: A

MH

Option A is correct because the maximum potential energy of a magnet in a magnetic field is given by MH, occurring when the magnet is anti-aligned with the field.

17 Medium

17 of 128

Remembering +4 | -1

The relation between

B,H\mathrm{\;and}\;I

in SI unit is

View answer and explanation

Correct option: A

B = {\mathrm{\mu }_0}\left( {H + I} \right)

Option A (

B = {\mathrm{\mu }_0}\left( {H + I} \right)

) is correct because it represents the relationship between magnetic induction (B), magnetizing field (H), and magnetization (I) in SI units.

18 Medium

18 of 128

Application +4 | -1

A magnet is parallel to a uniform magnetic field. If it is rotated by

60^\circ

, the work done is 0.8joules. How much additional work is done in moving it

30^\circ

further

View answer and explanation

Correct option: A

0.8 J

Option A is correct. The additional work done is the same as the initial work done (0.8 J) because the change in potential energy is the same for both rotations.

19 Medium

19 of 128

Understanding +4 | -1

All atoms of a magnetic substance have a
resultant magnetic moment even in absence of
external magnetic field. The substance is

View answer and explanation

Correct option: A

ferromagnetic

Option A (ferromagnetic) is correct because ferromagnetic substances retain a resultant magnetic moment even in the absence of an external magnetic field.

20 Medium

20 of 128

Remembering +4 | -1

Which of the following represents correct formula for magnetic flux?

View answer and explanation

Correct option: C

d \phi=\vec{B} \cdot \vec{d} s

Option C (

d \phi=\vec{B} \cdot \vec{d} s

) is correct because it represents the correct formula for magnetic flux as the dot product of the magnetic field vector and the area vector.

21 Medium

21 of 128

Understanding +4 | -1

A bar magnet is equivalent to

View answer and explanation

Correct option: C

Solenoid carrying current

Option C is correct because a solenoid carrying current produces a magnetic field similar to that of a bar magnet.

22 Medium

22 of 128

Understanding +4 | -1

The time period of a freely suspended magnet does not depend upon

View answer and explanation

Correct option: D

Length of the suspension

Option D is correct because the time period of a freely suspended magnet depends on its magnetic moment, moment of inertia, and the Earth's magnetic field, but not the length of the suspension.

23 Medium

23 of 128

Understanding +4 | -1

There is no couple acting when two bar
magnets are placed coaxially separated by a
distance because

View answer and explanation

Correct option: D

the forces act along the same line

Option D is correct because when two bar magnets are placed coaxially, the forces between their poles act along the same line, resulting in no net torque.

24 Medium

24 of 128

Understanding +4 | -1

For an isotropic medium

B,\;\mu ,\;H

and

M

are related as (where

B,\;{\mu _0},\;H

and

M

have their usual meanings in the context of magnetic material)

View answer and explanation

Correct option: D

B = {\mu _0}\left( {H + M} \right)

Option D is correct. The relationship between B, μ₀, H, and M for an isotropic medium is given by

B = {\mu _0}(H + M)

25 Medium

25 of 128

Analyzing +4 | -1

Assertion (A): Magnetic poles are only mathematical assumptions having no real existence.

Reason (R): A charged particle is moved along a magnetic field line. The magnetic force on the particle is perpendicular to its velocity.

View answer and explanation

Correct option: C

If (A) is true but the (R) is false

Option C is correct. Magnetic poles do exist in reality (as dipoles), and the reason is false because the magnetic force is perpendicular to both velocity and magnetic field, not just velocity.

26 Medium

26 of 128

Application +4 | -1

A small bar magnet of moment

M

is placed in a uniform field

H

. If magnet makes an angle of

30^\circ

with field, the torque acting on the magnet is

View answer and explanation

Correct option: B

\frac{{MH}}{2}

Option B (

\frac{{MH}}{2}

) is correct because the torque acting on the magnet is given by

\tau = MH\sin\theta

, and with

\theta = 30^\circ

\sin 30^\circ = \frac{1}{2}

27 Medium

27 of 128

Remembering +4 | -1

For a paramagnetic material, the dependence of the magnetic susceptibility

X

on the absolute temperature is given as

View answer and explanation

Correct option: C

X \propto 1/T

Option C (

X \propto 1/T

) is correct because the magnetic susceptibility of a paramagnetic material is inversely proportional to the absolute temperature, as described by Curie's Law.

28 Medium

28 of 128

Remembering +4 | -1

Electromagnets are made of soft iron because soft iron has

View answer and explanation

Correct option: C

High permeability and low retentivity

Option C (High permeability and low retentivity) is correct because soft iron's high permeability allows it to be easily magnetized, and its low retentivity ensures it quickly loses its magnetism when the current is turned off.

29 Medium

29 of 128

Application +4 | -1

A magnet of magnetic moment

50\hat i\;A

{m^2}

is placed along the

x

-axis in a magnetic field

\vec B = \left( {0.5\;\hat i + 3.0\hat j} \right)T

. The torque acting on the magnet is

View answer and explanation

Correct option: B

150\;\hat k\;N

m

Option B is correct because the torque is calculated using the cross product of the magnetic moment and the magnetic field, resulting in 150k N-m.

30 Medium

30 of 128

Understanding +4 | -1

Nickel shows ferromagnetic property at room temperature. If the temperature is increased beyond Curie temperature, then it will show

View answer and explanation

Correct option: A

Paramagnetism

Option A (Paramagnetism) is correct because above the Curie temperature, ferromagnetic materials lose their spontaneous magnetization and become paramagnetic.

Revision notes and key takeaways

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Key Takeaways

✓ This set contains 128 single-correct-answer MCQs on MAGNETISM AND MATTER.
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