MCQs of Magnetism and Matter

Magnetism and Matter MCQs

MCQs of Magnetism and Matter

Showing 101 to 110 out of 145 Questions

101.

A magnet is hung horizontally in the magnetic meridian by a wire without any twist. If the supporting wire is given a twist of 180° at the top, the magnet rotates by 30°. Now if another magnet is used, then a twist of 270° at the supporting end of wire also produces a rotation of the magnet by 30°. Compare the magnetic dipole moments of the two magnets.

(a)	$\frac{5}{8}$
(b)	$\frac{8}{5}$
(c)	$\frac{3}{8}$
(d)	$\frac{8}{3}$

102.

A magnet has coercivity of 3 × 10³ Am^-1. It is keep in a 10 cm long solenoid with a total of 50 turns. How much current has to be passed through the solenoid to demagnetize it ?

(a)	0.17 A
(b)	1.7 A
(c)	0.6 A
(d)	6 A

103.

There are 2.0 × 10²⁴ molecular dipoles in a paramagnetic salt. Each has dipole moment 1.5 × 10^-23 A m² (or J T^-1). This salt kept in a uniform magnetic field 0.84 T is cooled to a temperature of 4.2 K. In this case the magnetizaation acquired is 15 % of the saturation magnetization. What must be the dipole moment of this sample in magnetic field 0.98 T and at temperature of 2.8 K ? (Assume the applicability of Curie's law)

(a)	7.87 A m²
(b)	8.77 A m²
(c)	7.78 A m²
(d)	78.7 A m²

104.

The magnetic dipole moment of current carrying loop is _____ proportional to the length of the loop.

(a)	directly
(b)	inversely
(c)	directly square
(d)	inversely square

105.

A paramagnetic gas has 2.0 × 10²⁶ atoms/m³ with the atomic magnetic dipole moment of 1.5 × 10^-23 A m² each. The gas is at 27°C.(i) Find the maximum magnetization intensity of this sample.(ii) If the gas in this problem is kept inn a uniform magnetic field of 3.0 T, is it possible to achieve saturation magnetization ? Why ? [Hint : Thermal energy of an atom of gas is

\frac{3}{2} k_{B} T

, and maximum potential energy of the atom = mB. Find the ratio of thermal energy to the maximum potential energy and give answer.](k_B = 1.38 × 10^-23 J K^-1)

(a)	3 × 10^-3 Am^-1, saturation magnetization does not achieved
(b)	3 × 10³ Am^-1 saturation magnetization does not achieved
(c)	3 × 10³ Am^-1 saturation magnetization does achieved
(d)	3 × 10^-3 Am^-1 saturation magnetization does achieved

106.

A toroidal core with 3000 turns has inner and outer radii of 11 cm and 12 cm, respectiely. When a current of 0.70 A is passed, the magnetic field produced in the core is 2.5 T. Find the relative permeability of the core (μ₀ = 4π × 10^-7 T m A^-1)

(a)	685
(b)	865
(c)	568
(d)	658

107.

Two small and similar bar magnets have magnetic dipole moment of 1.0 Am² each. They are kept in a plane in such a way that their axes are perpendicular to each other. A line drawn through the axis of one magnet. If the distance between their centres is 2 m, find the magnetic field at the mid point of the line joining their centres.

(a)	$\sqrt{2} \times 10^{- 7} T$
(b)	$\sqrt{3} \times 10^{- 7} T$
(c)	$\sqrt{5} \times 10^{- 7} T$
(d)	$1 \times 10^{- 7} T$

108.

A magnetic pole of bar magnet with pole strength of 100 A m is 20 cm away from the centre of a bar magnet. Bar magnet has pole strength of 200 A m and has a length of 5 cm. If the magnetic pole is on the axis of the bar magnet, find the force on the magnetic pole.

(a)	2.5 × 10^-4 N
(b)	2.5 × 10^-2 N
(c)	5 × 10^-4 N
(d)	5 × 10^-2 N

109.

The work done for rotating a magnet with magnetic dipole moment m, by 90° from its magnetic meridian is n times the work done to rotate it by 60°, value of n _____.

(a)	$\sqrt{2}$
(b)	$\frac{1}{2}$
(c)	2
(d)	$\frac{1}{\sqrt{2}}$

110.

A magnet makes an angle of 45° with the horizontal in a plane making an angle of 30° with the magnetic meridian. The true value of the dip angle at the place is _____

(a)	tan^-1(0.866)
(b)	cot^-1(0.866)
(c)	sin^-1(0.866)
(d)	cos^-1(0.866)

Showing 101 to 110 out of 145 Questions