35 + Interview Questions in MAGNETIC MATERIALS IN GENERAL AWARENESS Page 1 InterviewSolution

1.	An electron in an atom revolves around the nucleus in an orbit of radius 0.5 Å. Calculate the equivalent magnetic moment if the frequency of revolution of the electron is 10 MHz.
Answer» Data : r = 0.5 Å = 5 × 10^-11 m, f = 10¹⁰ MHz = 10¹⁶ Hz, e = 1.6 × 10^-19C Equivalent current, I = \(\cfrac eT\) = ef The equivalent magnetic moment is M = IA = ef(πr²) = (1.6 × 10^-19)(1016)(3.142)(5 × 10^-11)² = 1.6 × 3.142 × 25 × 10^-25 = 1.257 × 10^-23 A∙m²

1.

An electron in an atom revolves around the nucleus in an orbit of radius 0.5 Å. Calculate the equivalent magnetic moment if the frequency of revolution of the electron is 10 MHz.

Answer»

Data : r = 0.5 Å = 5 × 10^-11 m,

f = 10¹⁰ MHz = 10¹⁶ Hz, e = 1.6 × 10^-19C

Equivalent current, I = \(\cfrac eT\) = ef

The equivalent magnetic moment is

M = IA = ef(πr²)

= (1.6 × 10^-19)(1016)(3.142)(5 × 10^-11)²

= 1.6 × 3.142 × 25 × 10^-25

= 1.257 × 10^-23 A∙m²

Discussion

2.	State the expression for the torque acting on a magnetic dipole in a uniform magnetic field.
Answer» When a magnetic dipole of magnetic dipole moment \(\vec M\) is placed in a uniform magnetic field of induction \(\vec B\), it experiences a torque whose magnitude is τ = MB sin θ where θ is the smaller angle between the magnetic axis and \(\vec B\). [Note: When the dipole is placed with its axis at right-angles to the field, i.e, θ = 90°, τ = MB or M = \(\cfrac{\tau}B\) This is the defining equation for the magnetic dipole moment.]

2.

State the expression for the torque acting on a magnetic dipole in a uniform magnetic field.

Answer»

When a magnetic dipole of magnetic dipole moment \(\vec M\) is placed in a uniform magnetic field of induction \(\vec B\), it experiences a torque whose magnitude is

τ = MB sin θ

where θ is the smaller angle between the magnetic axis and \(\vec B\).

[Note: When the dipole is placed with its axis at right-angles to the field, i.e, θ = 90°,

τ = MB or M = \(\cfrac{\tau}B\)

This is the defining equation for the magnetic dipole moment.]

Discussion

3.	There are different types of shielding available like electrical and accoustic shielding apart from magnetic shielding discussed above. Electrical insulator functions as an electrical barrier or shield and comes in a wide array of materials. Normally the electrical wires used in our households are also shielded. In case of audio recording it is necessary to reduce other stray sound which may interfere with the sound to be recorded. So the recording studios are sound insulated using acoustic material.
Answer» There are different types of shielding, such as electrical, electromagnetic. magnetic, RF (radio frequency) and acoustic, to shield a given space or sensitive instrument from unwanted fields of each type.

Discussion

4.	Find the magnitude of the magnetic moment of a magnet if a couple exerting torque 0.5 N.m is required to hold the magnet with its axis perpendicular to a uniform magnetic field of induction 2 × 10-3T
Answer» Data : τ = 0.5 N∙m, B = 2 × 10^-3T, θ = 90° τ = MB sin θ ∴ M = \(\cfrac{\tau}{B\,sin\theta}\) = \(\cfrac{0.5\,N.m}{(2\times10^{-3}T)sin \,90^\circ}\) = 250 A∙m² The magnitude of the magnetic moment of the magnet is 250 A∙m² .

4.

Find the magnitude of the magnetic moment of a magnet if a couple exerting torque 0.5 N.m is required to hold the magnet with its axis perpendicular to a uniform magnetic field of induction 2 × 10-3T

Answer»

Data : τ = 0.5 N∙m,

B = 2 × 10^-3T, θ = 90°

τ = MB sin θ

∴ M = \(\cfrac{\tau}{B\,sin\theta}\) = \(\cfrac{0.5\,N.m}{(2\times10^{-3}T)sin \,90^\circ}\)

= 250 A∙m²

The magnitude of the magnetic moment of the magnet is 250 A∙m² .

Discussion

5.	State any four properties of a diamagnetic material.
Answer» Properties of a diamagnetic material : 1. In the absence of an external magnetic field, the magnetic dipole moment of each atom / molecule of a diamagnetic material is zero. 2. A diamagnetic material is weakly repelled by a magnet. 3. If a thin rod of a diamagnetic material is suspended in a uniform magnetic field, it comes to rest with its length perpendicular to the field. 4. When placed in a nonuniform magnetic field, a diamagnetic material is repelled from the region of strong field. 5. The magnetic susceptibility (χ_m) of a diamagnetic material is small and negative. 6. χ_m is very nearly temperatureindependent. 7. The relative permeability (μ_r) of a diamagnetic material is slightly less than 1 and very nearly temperature independent. 8. If a diamagnetic liquid in a watch glass is placed on two closely spaced polepieces of a magnet, the liquid accumulates on the sides causing a depression at the centre. [ Note : When the pole-pieces are moved apart, the effect is reversed, i.e., the diamagnetic liquid accumulates at the centre, where the magnetic field is weak.] 9. A diamagnetic liquid in a U-tube placed in a magnetic field shows a depression in the arm to which the magnetic field is applied. 10. If a diamagnetic gas is introduced between the pole-pieces of a magnet, it spreads at right angles to the field.

5.

State any four properties of a diamagnetic material.

Answer»

Properties of a diamagnetic material :

1. In the absence of an external magnetic field, the magnetic dipole moment of each atom / molecule of a diamagnetic material is zero.

2. A diamagnetic material is weakly repelled by a magnet.

3. If a thin rod of a diamagnetic material is suspended in a uniform magnetic field, it comes to rest with its length perpendicular to the field.

4. When placed in a nonuniform magnetic field, a diamagnetic material is repelled from the region of strong field.

5. The magnetic susceptibility (χ_m) of a diamagnetic material is small and negative.

6. χ_m is very nearly temperatureindependent.

7. The relative permeability (μ_r) of a diamagnetic material is slightly less than 1 and very nearly temperature independent.

8. If a diamagnetic liquid in a watch glass is placed on two closely spaced polepieces of a magnet, the liquid accumulates on the sides causing a depression at the centre.

[ Note : When the pole-pieces are moved apart, the effect is reversed, i.e., the diamagnetic liquid accumulates at the centre, where the magnetic field is weak.]

9. A diamagnetic liquid in a U-tube placed in a magnetic field shows a depression in the arm to which the magnetic field is applied.

10. If a diamagnetic gas is introduced between the pole-pieces of a magnet, it spreads at right angles to the field.

Discussion

6.	What is diamagnetism?
Answer» A material which is weakly repelled by a magnet and whose atoms/molecules do not possess a net magnetic moment in the absence of an external magnetic field is called a diamagnetic material. When a diamagnetic material is placed in a mag-netic field, it acquires a small net induced magnetic moment directed opposite to the field. The induced magnetism exhibited by such materials is called diamagnetism.

Discussion

7.	Which magnetic materials have (i) relative permeability > 1 (ii) relative permeability <1?
Answer» (i) Both paramagnetic and ferromagnetic materials have relative permeability (μ_r ) greater than 1. μ_r is only slightly greater than 1 for a paramagnetic material. μ_r is very high for a ferromagnetic material and is a function of the magnetizing field (also called the magnetic field intensity). (ii) μ_r is slightly less than 1 for a diamagnetic material.

7.

Which magnetic materials have (i) relative permeability > 1 (ii) relative permeability <1?

Answer»

(i) Both paramagnetic and ferromagnetic materials have relative permeability (μ_r ) greater than 1. μ_r is only slightly greater than 1 for a paramagnetic material. μ_r is very high for a ferromagnetic material and is a function of the magnetizing field (also called the magnetic field intensity).

(ii) μ_r is slightly less than 1 for a diamagnetic material.

Discussion

8.	A bar magnet of magnetic length 0.12 m and pole strength 10 A-m is placed in a uniform magnetic field of induction 3 × 10-2 tesla. If the angle between the magnetic induction and the magnetic moment is 30°, find the magnitude of the torque acting on the magnet.
Answer» Data : 2l = 0.12 m, m = 10 A∙m, B = 3 × 10^-2 T, θ = 30° The magnitude of the torque, τ = MB sin θ = m (2l) B sin θ = (10 A∙m) (0.12 m)(3 × 10^-2T) sin 30° = 3.6 × 10^-2 × \(\cfrac12\) = 1.8 × 10^-2 N∙m

8.

A bar magnet of magnetic length 0.12 m and pole strength 10 A-m is placed in a uniform magnetic field of induction 3 × 10-2 tesla. If the angle between the magnetic induction and the magnetic moment is 30°, find the magnitude of the torque acting on the magnet.

Answer»

Data : 2l = 0.12 m,

m = 10 A∙m, B = 3 × 10^-2 T, θ = 30°

The magnitude of the torque,

τ = MB sin θ = m (2l) B sin θ

= (10 A∙m) (0.12 m)(3 × 10^-2T) sin 30°

= 3.6 × 10^-2 × \(\cfrac12\)

= 1.8 × 10^-2 N∙m

Discussion

9.	What is magnetic hysteresis ? Explain it on the basis of magnetic domains.
Answer» Magnetic hysteresis is a phenomenon shown by ferromagnetic materials in which the magnetic flux density through a material depends on the applied magnetizing field as well as the previous state of magnetization. Due to retention of its memory of previous state of magnetization, the flux density B lags behind (does not remain in step) with magnetizing field H. This delay in the change of its magnetization M (or equivalently, B) in response to a change in H is called hysteresis. Hysteresis can be understood through the concept of magnetic domains. Domain boundary displacements and domain rotations are not totally reversible. When the applied magnetizing field H is increased and then decreased back to its initial value, the domains do not return completely to their original configuration but retain some memory or history of their previous alignment.

9.

What is magnetic hysteresis ? Explain it on the basis of magnetic domains.

Answer»

Magnetic hysteresis is a phenomenon shown by ferromagnetic materials in which the magnetic flux density through a material depends on the applied magnetizing field as well as the previous state of magnetization. Due to retention of its memory of previous state of magnetization, the flux density B lags behind (does not remain in step) with magnetizing field H. This delay in the change of its magnetization M (or equivalently, B) in response to a change in H is called hysteresis.

Hysteresis can be understood through the concept of magnetic domains. Domain boundary displacements and domain rotations are not totally reversible. When the applied magnetizing field H is increased and then decreased back to its initial value, the domains do not return completely to their original configuration but retain some memory or history of their previous alignment.

Discussion

10.	What does the area inside the curve B – H (hysteresis curve) indicate?
Answer» A magnetic hysteresis loop is a closed curve obtained by plotting the magnetic flux density B of a ferromagnetic material against the corresponding magnetizing field H when the material is taken through a complete magnetizing cycle. The area enclosed by the loop represents the hysteresis loss per unit volume in taking the material through the magnetizing cycle.

Discussion

11.	What does the hysteresis loop represents?
Answer» A magnetic hysteresis loop is a closed curve obtained by plotting the magnetic flux density B of a ferromagnetic material against the corresponding magnetizing field H when the material is taken through a complete magnetizing cycle. The area enclosed by the loop represents the hysteresis loss per unit volume in taking the material through the magnetizing cycle.

Discussion

12.

Distinguish between a paramagnetic material and a ferromagnetic material.

Answer»

A paramagnetic material	A ferromagnetic material
1. The permanent atomic magnetic moments of a para‐ magnetic material are all randomly oriented so that, in the absence of an external magnetizing field, the material is unmagnetized.	1. The permanent atomic magnetic moments of a ferro‐ magnetic material interact strongly through exchange interaction forming domains which are spontaneously magnetized to saturation
2. It gets weakly magnetized when placed in an external magnetic field.	2. In an unmagnetized ma‐ terial, the directions of magnetization of the different domains are so oriented that the net magnetization is zero.
3. Its magnetization becomes zero when the external magnetic field is removed.	3. It retains some magnetization even after the external magnetic field is removed.
4. Its magnetization in a given external magnetic field increases with decreasing temperature. The magnetization reaches saturation only if the external field is very large and the temperature is very low.	4. It retains its domain structure only up to a characteristic Curie temperature, above which it becomes paramagnetic.
5. χ_m is small and positive. μ_r is slightly greater than 1.	5. χ_m and μ_r are positive and very high.

Discussion

13.	A magnetic dipole of magnetic moment 5 A∙m2 is placed in a uniform magnetic field of induction 10-3 T. Find the magnitude of the maximum torque acting on the dipole.
Answer» Data : M = 5 A∙m² , B = 10^-3T Torque, τ = MB sin θ The magnitude of the torque is maximum when θ = 90°. ∴ τ_max = MB = 5 × 10^-3 N∙m

13.

A magnetic dipole of magnetic moment 5 A∙m2 is placed in a uniform magnetic field of induction 10-3 T. Find the magnitude of the maximum torque acting on the dipole.

Answer»

Data : M = 5 A∙m² , B = 10^-3T

Torque, τ = MB sin θ

The magnitude of the torque is maximum

when θ = 90°.

∴ τ_max = MB = 5 × 10^-3 N∙m

Discussion

14.	Magnetic susceptibility for vacuum (where there is no matter) is (A) zero (B) positive (C) negative (D) infinite.
Answer» Correct option is (A) zero

Discussion

15.	The ratio of magnetization to magnetic field induction (M/B) for both diamagnetic and paramagnetic materials is, in the usual notation,(A) χm(B) \(\cfrac{X_m}{\mu_0}\)(C) µr (D) µ
Answer» Correct option is (B) \(\cfrac{X_m}{\mu_0}\)

Discussion

16.	When a parainagnetic material Is placed in a uniform magnetic field, (A) its atoms acquire a magnetic moment opposite to the magnetic field (B) the atomic magnetic moments tend to align along the magnetizing field (C) all the atomic magnetic moments align along the magnetizing field (D) the sample temporarily becomes ferromagnetic.
Answer» (B) the atomic magnetic moments tend to align along the magnetizing field

Discussion

17.	The dimensions of magnetic intensity are (A) [LI] (B) [L2 I] (C) [L-1 I] (D) [L-2 I].
Answer» Correct option is (C) [L^-1 I]

Discussion

18.	Which of the following is paramagnetic? (A) Bismuth (B) Copper (C) Liq. oxygen (D) Silver
Answer» (C) Liq. oxygen

Discussion

19.	Magnetizing and demagnetizing a material that has hysteresis involves (A) increase in the temperature of the material (B) a terro-to-para phase change (C) decrease in the temperature of the material (D) none of the above.
Answer» (A) increase in the temperature of the material

Discussion

20.	A thin, small gIas rod is suspended between the poles of a strung electromagnet. The rod (A) is strongly repelled by the magnetic field. (B) orients itself parallel to the magnetic field (C) orients itself perpendicuLar to the magnetic field (D) is weakly attracted by the magnetic field
Answer» (C) orients itself perpendicular to the magnetic field

Discussion

21.	The most exotic diamagnetic materials are (A) the glasses (B) the insulators (C) the superconductors (D) the semiconductors.
Answer» (C) the superconductors

Discussion

22.	Which of the following is diamagnetic? (A) Dysprosium (B) Gadolinium (C) Magnesium (D) Silver
Answer» Correct option is (D) Silver

Discussion

23.	Curie’s law is valid for (A) diamagnelics (B) paramagnetics (C) ferromagnetics (D) all materials,
Answer» (B) paramagnetics

Discussion

24.	A bar magnet 10 cm2 long has cross-sectional area 2 cm and magnetic dipole moment of 10 A∙m2 . The magnetization of its material, assumed to be uniform, is (A) 5 × 105 A/m (B) 2 × 105 A/m (C) 0.5 A/m (D) 0.2 A/m.
Answer» (A) 5 × 10⁵ A/m

Discussion

25.	A bar magnet of moment 10 A∙m2 is suspended such that it can rotate freely in a horizontal plane. The horizontal component of the Earth’s magnetic field at the place is 36 µT. Calculate the magnitude of the torque when its angular displacement with respect to the direction of the field is 8° and magnetic potential energy.
Answer» Data : M = 10 A∙m^2, B_h = 36 µT = 3.6 × 10^-5 T, θ = 8° The magnitude of the torque is τ = MB_h sin θ =(10)(3.6 × 10^-5)sin8° =(36 × 10^-5)(0.1391) = 5.007 × 10^-5 N∙m The magnetic potential energy of the bar magnet is U_θ = MB_h cos θ =(36 × 10^-5)cos8° =(36 × 10^-5)(0.99) = 3.564 × 10^-4 J

25.

A bar magnet of moment 10 A∙m2 is suspended such that it can rotate freely in a horizontal plane. The horizontal component of the Earth’s magnetic field at the place is 36 µT. Calculate the magnitude of the torque when its angular displacement with respect to the direction of the field is 8° and magnetic potential energy.

Answer»

Data : M = 10 A∙m^2,

B_h = 36 µT = 3.6 × 10^-5 T,

θ = 8°

The magnitude of the torque is

τ = MB_h sin θ

=(10)(3.6 × 10^-5)sin8°

=(36 × 10^-5)(0.1391) = 5.007 × 10^-5 N∙m

The magnetic potential energy of the bar magnet is

U_θ = MB_h cos θ

=(36 × 10^-5)cos8°

=(36 × 10^-5)(0.99) = 3.564 × 10^-4 J

Discussion

26.	A bar magnet of moment 10 A∙m is suspended such that it can rotate freely in a horizontal plane. The horizontal component of the Earth’s magnetic field at the place is 36 µT. Calculate the magnitude of the torque when its angular displacement with respect to the direction of the field is 8C and magnetic potential energy.
Answer» Data : M = 10 A∙m², B_h = 36µT = 3.6 × 10^-5 T, θ = 8° The magnitude of the torque is τ = MB_h sin θ = (10) (3.6 × 10^-5) sin 8° = (36 × 10^-5) (0.1391) = 5.007 × 10^-5 N∙m The magnetic potential energy of the bar magnet is U_θ = MB_h cos θ = (36 × 10^-5) cos 8° = (36 × 10^-5) (0.99) = 3.564 × 10^-4 J

26.

A bar magnet of moment 10 A∙m is suspended such that it can rotate freely in a horizontal plane. The horizontal component of the Earth’s magnetic field at the place is 36 µT. Calculate the magnitude of the torque when its angular displacement with respect to the direction of the field is 8C and magnetic potential energy.

Answer»

Data : M = 10 A∙m²,

B_h = 36µT = 3.6 × 10^-5 T,

θ = 8°

The magnitude of the torque is

τ = MB_h sin θ

= (10) (3.6 × 10^-5) sin 8°

= (36 × 10^-5) (0.1391) = 5.007 × 10^-5 N∙m

The magnetic potential energy of the bar magnet is

U_θ = MB_h cos θ

= (36 × 10^-5) cos 8°

= (36 × 10^-5) (0.99) = 3.564 × 10^-4 J

Discussion

27.	The length of a bar magnet is large compared to its width and breadth. The time period of its angular oscillation in a vibration magnetometer is 2s. The magnet is cut along its length into two equal parts and the two parts are then mounted together in the magnetometer with their like poles together. The time period of this combination will be (A) 2 s (B) 1 s(C) \(\cfrac12\)s(D) \(\cfrac1{\sqrt2}\)s
Answer» Correct option is (B) 1 s

Discussion

28.	A bar magnet made of steel has magnetic moment 2.5 A∙m2 and mass 6.6 × 10-3 kg. Given that the density of steel is 7.9 × 103 kg/m3, find the intensity of magnetization of the magnet.
Answer» Data : M = 2.5 A∙m², m = 6.6 × 10^-3 kg, ρ = 7.9 × 10³ kg/m³ Volume, V = \(\cfrac{m}\rho\) The intensity of magnetization of the magnet is M_z = M ∙ \(\cfrac{\rho}m\) = 2.5 x \(\cfrac{M}V\) = 2.992 × 10⁶ A/m [Note : Intensity of magnetization = magnetization.]

28.

A bar magnet made of steel has magnetic moment 2.5 A∙m2 and mass 6.6 × 10-3 kg. Given that the density of steel is 7.9 × 103 kg/m3, find the intensity of magnetization of the magnet.

Answer»

Data : M = 2.5 A∙m²,

m = 6.6 × 10^-3 kg,

ρ = 7.9 × 10³ kg/m³

Volume, V = \(\cfrac{m}\rho\)

The intensity of magnetization of the magnet is

M_z = M ∙ \(\cfrac{\rho}m\)

= 2.5 x \(\cfrac{M}V\) = 2.992 × 10⁶ A/m

[Note : Intensity of magnetization = magnetization.]

Discussion

29.	A rectangular bar magnet-with sides l. b and w – h.is mass n and magnetic moment M. It is free to rotate about a vertical axis through its centre of mass such that its faces of area l × b are honzoritaL The period T of angular oscillations of this magnet in a uniform magnetic field B is given by(A) \(\cfrac1{2\pi}\)\(\sqrt{\cfrac{12MB}{m(I^2+b^2)}}\)(B) \(\sqrt{\cfrac{\pi^2m(I^2+b^2)}{3MB}}\)(C) \(\sqrt{\cfrac{m(I^2+b^2)}{3MB}}\)(D) \(\sqrt{\cfrac{\pi^2M(I^2+b^2)}{3mB}}\)
Answer» Correct option is (B) \(\sqrt{\cfrac{\pi^2m(I^2+b^2)}{3MB}}\)

Discussion

30.	If the frequency of revolution of a proton (q = 1.6 × 10-19C) in a uniform magnetic induction is 106 Hz, what is the corresponding electric current?
Answer» I = \(\cfrac{q}T\) = qf = (1.6 × 10^-19)(10⁶) = 1.6 × 10^-13 A is the corresponding electric current.

30.

If the frequency of revolution of a proton (q = 1.6 × 10-19C) in a uniform magnetic induction is 106 Hz, what is the corresponding electric current?

Answer»

I = \(\cfrac{q}T\) = qf = (1.6 × 10^-19)(10⁶)

= 1.6 × 10^-13 A

is the corresponding electric current.

Discussion

31.	The frequency of revolution of the electron in the second Bohr orbit in the hydrogen atom is 8.22 × 1014 Hz. What is the corresponding electric ’ current? [e = 1.6 × 10-19 C]
Answer» I = \(\cfrac eT\) = ef = (1.6 × 10^-19)(8.22 × 10¹⁴) = 1.315 × 10^-4 A is the corresponding electric current.

31.

The frequency of revolution of the electron in the second Bohr orbit in the hydrogen atom is 8.22 × 1014 Hz. What is the corresponding electric ’ current? [e = 1.6 × 10-19 C]

Answer»

I = \(\cfrac eT\) = ef

= (1.6 × 10^-19)(8.22 × 10¹⁴)

= 1.315 × 10^-4 A

is the corresponding electric current.

Discussion

32.	What is the magnetic moment of an electron due to its orbital motion?
Answer» The orbital magnetic moment of an electron, of charge e and revolving with speed v in an orbit of radius r, is \(\cfrac12\) evr.

Discussion

33.	What is the gyromagnetic ratio of an orbital electron ? State its dimensions and the SI unit.
Answer» The ratio of the magnitude of the orbital magnetic moment to that of the orbital angular momentum of an electron in an atom is called its gyromagnetic ratio γ₀. If \(\vec M\)₀is the orbital magnetic moment of the electron with orbital angular momentum \(\vec L_0\), where e and me are the electronic charge and electron mass, respectively. Dimensions : [γ₀] = \(\cfrac{[charge]}{[mass]}\) = \(\cfrac{[TI]}{[M]}\) = M^-1 TI] SI unit : The coulomb per kilogram (C/kg). [Note : γ₀ = 8.794 × 10¹⁰ C/kg. The gyromagnetic ratio of electron spin is nearly twice that of an orbital electron.]

33.

What is the gyromagnetic ratio of an orbital electron ? State its dimensions and the SI unit.

Answer»

The ratio of the magnitude of the orbital magnetic moment to that of the orbital angular momentum of an electron in an atom is called its gyromagnetic ratio γ₀. If \(\vec M\)₀is the orbital magnetic moment of the electron with orbital angular momentum \(\vec L_0\),

where e and me are the electronic charge and electron mass, respectively.

Dimensions : [γ₀] = \(\cfrac{[charge]}{[mass]}\) = \(\cfrac{[TI]}{[M]}\) = M^-1 TI]

SI unit : The coulomb per kilogram (C/kg).

[Note : γ₀ = 8.794 × 10¹⁰ C/kg. The gyromagnetic ratio of electron spin is nearly twice that of an orbital electron.]

Discussion

34.	A coil has 1000 turns, each of area 0.5 m2. What is the magnetic moment of the coil when it carries a current of 1 mA ?
Answer» Magnetic moment M = NIA = 1000 × 1 × 10^-3 × 0.5 = 0.5 A∙m²

34.

A coil has 1000 turns, each of area 0.5 m2. What is the magnetic moment of the coil when it carries a current of 1 mA ?

Answer»

Magnetic moment M = NIA

= 1000 × 1 × 10^-3 × 0.5

= 0.5 A∙m²

Discussion

35.	A current-carrying coil with magnetic moment \(\vec M\) (M = 5 A∙m2) is placed in a uniform magnetic field of induction \(\vec B\) (B = 0.2 Wb/m2) such that the angle between \(\vec M\) and \(\vec B\) is 30°. What is the torque acting on the coil ?
Answer» τ = MB sin θ = (5) (0.2) sin 30° = 0.5 N∙m is the torque acting on the coil.

35.

A current-carrying coil with magnetic moment \(\vec M\) (M = 5 A∙m2) is placed in a uniform magnetic field of induction \(\vec B\) (B = 0.2 Wb/m2) such that the angle between \(\vec M\) and \(\vec B\) is 30°. What is the torque acting on the coil ?

Answer»

τ = MB sin θ = (5) (0.2) sin 30° = 0.5 N∙m is

the torque acting on the coil.

Discussion

Explore topic-wise InterviewSolutions in .

An electron in an atom revolves around the nucleus in an orbit of radius 0.5 Å. Calculate the equivalent magnetic moment if the frequency of revolution of the electron is 10 MHz.

State the expression for the torque acting on a magnetic dipole in a uniform magnetic field.

Find the magnitude of the magnetic moment of a magnet if a couple exerting torque 0.5 N.m is required to hold the magnet with its axis perpendicular to a uniform magnetic field of induction 2 × 10-3T

State any four properties of a diamagnetic material.

What is diamagnetism?

Which magnetic materials have (i) relative permeability &gt; 1 (ii) relative permeability &lt;1?

A bar magnet of magnetic length 0.12 m and pole strength 10 A-m is placed in a uniform magnetic field of induction 3 × 10-2 tesla. If the angle between the magnetic induction and the magnetic moment is 30°, find the magnitude of the torque acting on the magnet.

What is magnetic hysteresis ? Explain it on the basis of magnetic domains.

What does the area inside the curve B – H (hysteresis curve) indicate?

What does the hysteresis loop represents?

Distinguish between a paramagnetic material and a ferromagnetic material.

A magnetic dipole of magnetic moment 5 A∙m2 is placed in a uniform magnetic field of induction 10-3 T. Find the magnitude of the maximum torque acting on the dipole.

Magnetic susceptibility for vacuum (where there is no matter) is (A) zero (B) positive (C) negative (D) infinite.

The ratio of magnetization to magnetic field induction (M/B) for both diamagnetic and paramagnetic materials is, in the usual notation,(A) χm(B) \(\cfrac{X_m}{\mu_0}\)(C) µr (D) µ

The dimensions of magnetic intensity are (A) [LI] (B) [L2 I] (C) [L-1 I] (D) [L-2 I].

Which of the following is paramagnetic? (A) Bismuth (B) Copper (C) Liq. oxygen (D) Silver

Magnetizing and demagnetizing a material that has hysteresis involves (A) increase in the temperature of the material (B) a terro-to-para phase change (C) decrease in the temperature of the material (D) none of the above.

A thin, small gIas rod is suspended between the poles of a strung electromagnet. The rod (A) is strongly repelled by the magnetic field. (B) orients itself parallel to the magnetic field (C) orients itself perpendicuLar to the magnetic field (D) is weakly attracted by the magnetic field

The most exotic diamagnetic materials are (A) the glasses (B) the insulators (C) the superconductors (D) the semiconductors.

Which of the following is diamagnetic? (A) Dysprosium (B) Gadolinium (C) Magnesium (D) Silver

Curie’s law is valid for (A) diamagnelics (B) paramagnetics (C) ferromagnetics (D) all materials,

A bar magnet 10 cm2 long has cross-sectional area 2 cm and magnetic dipole moment of 10 A∙m2 . The magnetization of its material, assumed to be uniform, is (A) 5 × 105 A/m (B) 2 × 105 A/m (C) 0.5 A/m (D) 0.2 A/m.

A bar magnet made of steel has magnetic moment 2.5 A∙m2 and mass 6.6 × 10-3 kg. Given that the density of steel is 7.9 × 103 kg/m3, find the intensity of magnetization of the magnet.

If the frequency of revolution of a proton (q = 1.6 × 10-19C) in a uniform magnetic induction is 106 Hz, what is the corresponding electric current?

The frequency of revolution of the electron in the second Bohr orbit in the hydrogen atom is 8.22 × 1014 Hz. What is the corresponding electric ’ current? [e = 1.6 × 10-19 C]

What is the magnetic moment of an electron due to its orbital motion?

What is the gyromagnetic ratio of an orbital electron ? State its dimensions and the SI unit.

A coil has 1000 turns, each of area 0.5 m2. What is the magnetic moment of the coil when it carries a current of 1 mA ?

A current-carrying coil with magnetic moment \(\vec M\) (M = 5 A∙m2) is placed in a uniform magnetic field of induction \(\vec B\) (B = 0.2 Wb/m2) such that the angle between \(\vec M\) and \(\vec B\) is 30°. What is the torque acting on the coil ?

Which magnetic materials have (i) relative permeability > 1 (ii) relative permeability <1?