If a magnetic dipole of dipole moment $M$ rotated through an angle ${\rm{\theta }}$ with respect to the direction of the field $H$, then the work done is

$MH\left( {1 - \cos {\rm{\theta }}} \right)$

$MH\left( {1 - \sin {\rm{\theta }}} \right)$

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NEET • PHYSICS • MAGNETISM AND MATTER

Magnetism and matter practice · Mixed difficulty

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Showing 151-164 of 164 questions

151 Medium

151 of 164

Understanding +4 | -1

A bar magnet has magnetic moment

M

. If a hole is drilled normally through the centre of length of magnet, then the new magnetic moment of the magnet is

View answer and explanation

Correct option: A

Less than

M

Option A (Less than

M

) is correct because removing material from the magnet reduces its overall magnetic moment.

152 Medium

152 of 164

Application +4 | -1

Magnetic moment of bar magnet is

M

. The work done to turn the magnet by

90^\circ

of magnet in direction of magnetic field

B

will be

View answer and explanation

Correct option: D

MB

Option D is correct because the work done to turn the magnet by 90° is given by MB(cosθ₁ - cosθ₂), where θ₁ = 0° and θ₂ = 90°, resulting in MB.

153 Medium

153 of 164

Understanding +4 | -1

Due to the earth’s magnetic field, charged cosmic ray particles

View answer and explanation

Correct option: C

Can never reach the equator

Option A (Require greater kinetic energy to reach the equator than the poles) is correct because charged particles are deflected by the Earth's magnetic field, and this deflection is greatest at the equator.

154 Easy

154 of 164

Application +4 | -1

A bar magnet of length

10cm

and pole strength

2\,Am

makes an angle

60^\circ

with a uniform magnetic field of induction

50T

. The couple acting on it is

View answer and explanation

Correct option: A

5\sqrt 3 Nm

Option A is correct because the torque is calculated using the formula τ = MBLsinθ, where L is the length, and substituting the given values yields 5√3 Nm.

155 Hard

155 of 164

Application +4 | -1

A vibration magnetometer placed in magnetic meridian has small bar magnet. The magnet executes oscillations with a time period of

2 \, \mathrm{sec}

in earth's horizontal magnetic field of

36 \, \mu \mathrm{T}

. When a horizontal magnetic field '

B

' is produced opposite to the earth's field by placing a current carrying wire, the new time period of magnet is

6 \, \mathrm{sec}

. Then value of '

{B}

' is:

View answer and explanation

Correct option: D

32 \mu \mathrm{T}

Option D (

32 \mu \mathrm{T}

) is correct because it involves calculating the magnetic field produced by the wire using the time periods of oscillation.

156 Medium

156 of 164

Application +4 | -1

If a magnetic dipole of dipole moment

M

rotated through an angle

\mathrm{\theta }

with respect to the direction of the field

H

, then the work done is

View answer and explanation

Correct option: D

MH\left( {1 - \cos \mathrm{\theta }} \right)

Option D (

MH\left( {1 - \cos \mathrm{\theta }} \right)

) is correct because it represents the work done in rotating a magnetic dipole in a magnetic field.

157 Medium

157 of 164

Remembering +4 | -1

Curie temperature is the one above which

View answer and explanation

Correct option: D

Ferromagnetic changes to paramagnetic

Option D (Ferromagnetic changes to paramagnetic) is correct because above the Curie temperature, ferromagnetic materials lose their spontaneous magnetization and become paramagnetic.

158 Medium

158 of 164

Analyzing +4 | -1

Using a bar magnet

P

, a vibration magnetometer has time period

2seconds

. When a bar

Q

(identical to

P

in mass and size) is placed on top of

P

, the time period is unchanged. Which of the following statements is true

View answer and explanation

Correct option: B

Q

is a bar magnet identical to

P

, and its north pole is placed on top of

P'

s north pole

Option B (

Q

is a bar magnet identical to

P

, and its north pole is placed on top of

P

's north pole) is correct because the time period remains unchanged, implying the effective magnetic moment doubles, which only happens when identical magnets are aligned.

159 Medium

159 of 164

Understanding +4 | -1

Among the following properties describing diamagnetism identify the property that is wrongly stated

View answer and explanation

Correct option: C

Diamagnetic materials have a small positive susceptibility

Option C is correct. Diamagnetic materials have a small negative susceptibility, not a positive one.

160 Easy

160 of 164

Application +4 | -1

A bar magnet of magnetic moment

2A{m^2}

is free to rotate about a vertical axis passing through its centre. The magnet is released from rest from east – west position. Then the K.E of the magnet as it takes N – S position is

\left[ {{B_H} = 25\mu T} \right]

View answer and explanation

Correct option: B

50\mu J

Option B (

50\mu J

) is correct because the kinetic energy gained equals the potential energy lost as the magnet aligns with the field.

161 Medium

161 of 164

Understanding +4 | -1

When a magnet is placed vertically on horizontal board, number of neutral points obtained on the board is

View answer and explanation

Correct option: D

One

Option D (One) is correct because when a magnet is placed vertically, there is only one neutral point on the horizontal board, which lies on the equatorial line.

162 Medium

162 of 164

Analyzing +4 | -1

Assertion (A): Time period of vibrations of a pair of magnets in sum position is always smaller than in difference position.

Reason (R):

\mathrm{T}=2 \pi \sqrt{I / M B_H}

, where symbols have their standard meaning.

View answer and explanation

Correct option: A

If both (A) and (R) are true and the (R) is a correct explanation of the (A)

Option A (If both (A) and (R) are true and the (R) is a correct explanation of the (A)) is correct because the time period is inversely proportional to the magnetic moment, which is greater in the sum position.

163 Medium

163 of 164

Application +4 | -1

A compass needle placed at a distance

r

from a short magnet in a tan

A

position shows a deflection of 60

^ \circ

. If the distance is increased to

r{\left( 2 \right)^{1/3}}

, the deflection of compass needle is

View answer and explanation

Correct option: A

^ \circ

Option A (30

^ \circ

) is correct because the magnetic field due to a short magnet varies inversely with the cube of the distance.

164 Medium

164 of 164

Understanding +4 | -1

Assertion (A): The direction of magnetic moment and orbital angular momentum are opposite to each other for electron.

Reason (R): Electron is negatively charged.

View answer and explanation

Correct option: A

If both (A) and (R) are true and the (R) is a correct explanation of the (A)

Option A is correct because the direction of magnetic moment and orbital angular momentum are opposite for an electron due to its negative charge, making the reason a correct explanation.

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