A magnetic dipole is placed in two perpendicular magnetic fields ${{\rm{\vec B}}}$ and ${{\rm{\vec H}}}$ and is in equilibrium taking angle ${\rm{\theta }}$ with ${{\rm{\vec B}}}$. Then

$B\sin {\rm{\theta }} = H\cos {\rm{\theta }}$

$B\;{\rm{cos\theta }} = H\sin {\rm{\theta }}$

Relative permittivity and permeability of a material are ${{\rm{\varepsilon }}_r}$ and ${{\rm{\mu }}_r},$ respectively. Which of the following values of these quantities are allowed for a diamagnetic material?

${\varepsilon _r} = 1.5,\;{{\rm{\mu }}_r} = 0.5$

${\varepsilon _r} = 0.5,\;{{\rm{\mu }}_r} = 1.5$

${\varepsilon _r} = 0.5,{{\rm{\mu }}_r} = 0.5$

${\varepsilon _r} = 1.5,{{\rm{\mu }}_r} = 1.5$

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NEET • PHYSICS • MAGNETISM AND MATTER

Magnetism and matter practice · Medium

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31 Medium

31 of 128

Application +4 | -1

The radius of the coil of a tangent galvanometer which has 10 turns is 0.1 m. The current required to produce a deflection of

60^\circ \;\left( {{B_H} = 4 \times {{10}^{ - 5}}\mathrm{\;T}} \right)

View answer and explanation

Correct option: B

1.1 A

Option B (1.1 A) is correct because it is the current calculated using the tangent galvanometer formula with the given parameters.

32 Medium

32 of 128

Understanding +4 | -1

When the N- pole of a bar magnet points
towards the south and S- pole towards the
north, the null point are at the

View answer and explanation

Correct option: A

magnetic axis

Option A (magnetic axis) is correct because when the poles are reversed relative to Earth's magnetic field, the null points lie along the magnetic axis.

33 Medium

33 of 128

Remembering +4 | -1

If a diamagnetic substance is brought near north or south pole of a bar magnet, it is

View answer and explanation

Correct option: B

Repelled by the poles

The correct answer is B (Repelled by the poles) because diamagnetic substances are repelled by magnetic fields.

34 Medium

34 of 128

Remembering +4 | -1

The magnetic field due to a small magnetic dipole of magnetic moment

M

, at distance

r

from the centre on the equatorial line is given by (in M.K.S system)

View answer and explanation

Correct option: B

\frac{{{\mu _0}}}{{4\pi }} \times \frac{M}{{{r^3}}}

Option B (

\frac{{{\mu _0}}}{{4\pi }} \times \frac{M}{{{r^3}}}

) is correct because it represents the magnetic field due to a small magnetic dipole at a distance r on the equatorial line.

35 Medium

35 of 128

Application +4 | -1

The effective length of a magnet is 31.4 cm and its pole strength is 0.5 Am. Calculate its magnetic moment. If it is bent in form of semicircle, then magnetic moment will be

View answer and explanation

Correct option: A

0.157\mathrm{\;A}{\mathrm{m}^2},\mathrm{\;}0.01\mathrm{\;A}{\mathrm{m}^2}

Option A (

0.157\mathrm{\;A}{\mathrm{m}^2},\mathrm{\;}0.01\mathrm{\;A}{\mathrm{m}^2}

) is correct because the magnetic moment is calculated as

M = m \times l

initially and then

M' = m \times (2r)

where

r = l/\pi

when bent into a semicircle.

36 Medium

36 of 128

Application +4 | -1

A paramagnetic substance of susceptibility

3\mathrm{ } \times \mathrm{ }{10^{ - 4}}

is placed in a magnetic intensity of

4\mathrm{ } \times \mathrm{ }{10^{ - 4}}A{m^{ - 1}}

. Then the intensity of magnetization (in the units of

A{m^{ - 1}}

) is

View answer and explanation

Correct option: C

12 \times {10^{ - 8}}

Option C (

12 \times {10^{ - 8}}

) is correct because the intensity of magnetization is the product of susceptibility and magnetic intensity.

37 Medium

37 of 128

Remembering +4 | -1

The intensity of magnetic field due to an isolated pole of strength

m

at a point distance

r

from it will be

View answer and explanation

Correct option: A

\frac{m}{{{r^2}}}

Option A (

\frac{m}{{{r^2}}}

) is correct because the intensity of the magnetic field due to an isolated pole is inversely proportional to the square of the distance.

38 Medium

38 of 128

Application +4 | -1

A short bar magnet experiences a torque of magnitude 0.64 J. When it is placed in a uniform magnetic field of 0.32 T, taking an angle of  with the direction of the field. The magnetic moment of the magnet is

View answer and explanation

Correct option: B

4\mathrm{\;A}{\mathrm{m}^2}

Option B is correct because the magnetic moment is calculated using the formula τ = MBsinθ, and substituting the given values yields 4 Am².

39 Medium

39 of 128

Application +4 | -1

A magnetised wire is bent into an arc of a circle subtending an angle

60^\circ

at its centre. Then its magnetic moment is X. If the same wire is bent into an arc of a circle subtending an angle

90^\circ

at its centre then its magnetic moment will be

View answer and explanation

Correct option: C

\frac{{\left( {2\sqrt 2 } \right)x}}{3}

Option C is correct because the magnetic moment is proportional to sin(

\theta

/2), and the ratio of magnetic moments for 60° and 90° arcs is (2√2)/3.

40 Medium

40 of 128

Understanding +4 | -1

Which of the following properties is 'False' for
a bar magnet ?

View answer and explanation

Correct option: A

It doesn't produce magnetic field

Option A (It doesn't produce magnetic field) is the false statement because a bar magnet inherently produces a magnetic field.

41 Medium

41 of 128

Understanding +4 | -1

Which of the following is represented by the area enclosed by a hysteresis loop (

B - H

curve)?

View answer and explanation

Correct option: C

Heat energy lost per unit volume in the sample

Option C is correct. The area enclosed by the hysteresis loop represents the energy lost as heat per unit volume during each magnetization cycle.

42 Medium

42 of 128

Application +4 | -1

A magnetic dipole is placed in two perpendicular magnetic fields

{\mathrm{\vec B}}

and

{\mathrm{\vec H}}

and is in equilibrium taking angle

\mathrm{\theta }

with

{\mathrm{\vec B}}

. Then

View answer and explanation

Correct option: C

B\sin \mathrm{\theta } = H\cos \mathrm{\theta }

Option C (

B\sin \mathrm{\theta } = H\cos \mathrm{\theta }

) is correct because the torques due to the two magnetic fields must balance for equilibrium.

43 Medium

43 of 128

Understanding +4 | -1

The effect due to uniform magnetic field on a freely suspended magnetic needle is as follows

View answer and explanation

Correct option: B

Torque is present but no net force

Option B is correct because a uniform magnetic field exerts a torque on a magnetic needle to align it with the field, but the net force is zero due to the uniformity of the field.

44 Medium

44 of 128

Understanding +4 | -1

Relative permittivity and permeability of a material are

{\mathrm{\varepsilon }_r}

and

{\mathrm{\mu }_r},

respectively. Which of the following values of these quantities are allowed for a diamagnetic material?

View answer and explanation

Correct option: B

{\varepsilon _r} = 1.5,\;{\mathrm{\mu }_r} = 0.5

Option B is correct. For a diamagnetic material, the relative permittivity can be greater than 1, and the relative permeability must be less than 1.

45 Medium

45 of 128

Remembering +4 | -1

Magnetic intensity for an axial point due to a short bar magnet of magnetic moment

M

is given by

View answer and explanation

Correct option: C

\frac{{{\mu _0}}}{{2\pi }} \times \frac{M}{{{d^3}}}

Option C (

\frac{{{\mu _0}}}{{2\pi }} \times \frac{M}{{{d^3}}}

) is correct because it represents the magnetic field intensity for an axial point due to a short bar magnet.

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46 Medium

46 of 128

Understanding +4 | -1

The time period of a bar magnet suspended horizontally in the earth’s magnetic field and allowed to oscillate

View answer and explanation

Correct option: A

Is directly proportional to the square root of its mass

Option A is correct because the time period of a bar magnet is directly proportional to the square root of its moment of inertia, which is related to its mass.

47 Medium

47 of 128

Understanding +4 | -1

A magnetic dipole is placed in a uniform magnetic field. The net magnetic force on the dipole

View answer and explanation

Correct option: A

Is always zero

Option A (Is always zero) is correct because in a uniform magnetic field, the forces on the north and south poles of the dipole are equal and opposite, resulting in a net force of zero.

48 Medium

48 of 128

Understanding +4 | -1

Curie-Weiss law is obeyed by iron

View answer and explanation

Correct option: D

Above Curie temperature

Option D is correct. The Curie-Weiss law describes the behavior of magnetic susceptibility above the Curie temperature, where the material transitions from ferromagnetic to paramagnetic.

49 Medium

49 of 128

Understanding +4 | -1

A magnetic needle is kept in a non-uniform magnetic field. It experiences force and torque both due to unequal forces acting on poles.

View answer and explanation

Correct option: C

A force and a torque

Option C (A force and a torque) is correct because in a non-uniform magnetic field, a magnetic needle experiences both a force and a torque due to the unequal forces acting on its poles.

50 Medium

50 of 128

Understanding +4 | -1

Keeping dissimilar poles of two magnets of equal pole strength and length same side, their time period will be

View answer and explanation

Correct option: C

Infinity

Option C (Infinity) is correct because when dissimilar poles are kept together, the net magnetic moment is nearly zero, leading to an infinite time period.

51 Medium

51 of 128

Analyzing +4 | -1

Assertion(A): Steel is attracted by a magnet.

Reason (R): Steel is not a magnetic substance.

View answer and explanation

Correct option: C

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

Option C is correct because steel is attracted by a magnet, but it is a ferromagnetic substance, meaning it *is* a magnetic substance.

52 Medium

52 of 128

Remembering +4 | -1

The magnetic susceptibility of paramagnetic materials is

View answer and explanation

Correct option: D

Positive, but small

Option D (Positive, but small) is correct because paramagnetic materials have a small positive susceptibility, indicating they are weakly attracted to magnetic fields.

53 Medium

53 of 128

Understanding +4 | -1

Intensity of magnetic field due to earth at a point inside a hollow steel box is

View answer and explanation

Correct option: D

Zero

Option D (Zero) is correct because a hollow steel box acts as a magnetic shield, preventing the external magnetic field from penetrating inside.

54 Medium

54 of 128

Application +4 | -1

At a certain place the horizontal component of the earth’s magnetic field is

{B_0}

and the angle of dip is 45

^ \circ

. The total intensity of the field at that place will be

View answer and explanation

Correct option: B

\sqrt 2

{B_0}

Option B (

\sqrt 2

{B_0}

) is correct because the total intensity is related to the horizontal component and the angle of dip by

B = \frac{B_0}{\cos{\delta}}

55 Medium

55 of 128

Application +4 | -1

The magnetic susceptibility of a material of a rod is 499. The absolute permeability of vacuum is

4\pi \times {10^{ - 7}}\;\mathrm{H}{\mathrm{m}^{ - 1}}

. The absolute permeability of the material of a rod is

View answer and explanation

Correct option: B

2\pi \times {10^{ - 4}}\;\mathrm{H}{\mathrm{m}^{ - 1}}

Option B (

2\pi \times {10^{ - 4}}\;\mathrm{H}{\mathrm{m}^{ - 1}}

) is correct because it is calculated using the formula for absolute permeability:

\mu = \mu_0(1 + \chi_m)

56 Medium

56 of 128

Remembering +4 | -1

Magnetic field intensity is defined as

View answer and explanation

Correct option: B

Magnetic induction force acting on a unit magnetic pole

The correct answer is Magnetic induction force acting on a unit magnetic pole because magnetic field intensity (H) is defined as the force experienced by a unit north pole placed in the magnetic field.

57 Medium

57 of 128

Remembering +4 | -1

The field due to a magnet at a distance

R

from the centre of the magnet is proportional to

View answer and explanation

Correct option: D

{R^3}

Option D (1/

{R^3}

) is correct because the magnetic field due to a dipole falls off as the inverse cube of the distance.

58 Medium

58 of 128

Understanding +4 | -1

A vertical pillar of soft iron partially embedded in earth, at south pole, is found to be magnetized by the earth's magnetic field. The polarity at the top end of the pillar will be

View answer and explanation

Correct option: B

North pole

Option B is correct. The top end of the soft iron pillar will be a North pole because the Earth's magnetic field lines enter the Earth at the North pole and exit at the South pole. The pillar acts as a temporary magnet.

59 Medium

59 of 128

Application +4 | -1

Two magnets held together in earth’s magnetic field with same polarity together make 12

\mathrm{vib } - {\min ^{ - 1}}\mathrm{and}

when opposite poles together make 4

\mathrm{vib } - {\min ^{ - 1}}.\mathrm{The}

ratio of magnetic moments is

View answer and explanation

Correct option: D

10\mathrm{ }:\mathrm{ }8

Option D (

10\mathrm{ }:\mathrm{ }8

) is correct because the frequency of vibration is related to the magnetic moments and the earth's magnetic field.

60 Medium

60 of 128

Remembering +4 | -1

If the magnetic susceptibility of a specimen is small and positive, then the specimen is

View answer and explanation

Correct option: B

Paramagnetic

Option B (Paramagnetic) is correct because paramagnetic materials have a small, positive magnetic susceptibility.

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