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Right option is (a) Magnetic moment and magnetic FIELD are antiparallel

Best explanation: A magnetic DIPOLE POSSESS maximum potential energy when its magnetic moment and the magnetic field are antiparallel. When the magnetic dipole is aligned along the magnetic field, i.e. when θ = 180^0, it is in UNSTABLE equilibrium having maximum potential energy.

The correct OPTION is (a) Diamagnetic materials

For explanation: Diamagnetic materials are those which when placed in a magnetizing field are feebly magnetized in a DIRECTION OPPOSITE to that of the magnetizing field. Therefore, it is feebly REPELLED by a magnet. Example: zinc, gold, etc.

The correct OPTION is (a) 7 T

Easy explanation: GIVEN: permeability (μo) = 0.1 H/m; Magnetic intensity (H) = 70 A/m

Required equation ➔ Magnetic induction (B) = μo × H

B = 0.1 × 70

B = 7 T

Therefore, the magnetic induction inside the MATERIAL is 7 T.

Right choice is (a) True

The best explanation: Both MAGNETIZATION and magnetic intensity have the same unit ➔ A/m.

Magnetic intensity (H) = \(\frac {B_o}{\mu_o}\)B = \(\frac {current}{length}\) (ampere circuital LAW) ➔ unit of B0 = \(\frac {A}{m}\); μ0 is DIMENSIONLESS as it is a constant. THEREFORE, the unit of H is the same as B0.

Magnetization (I) = \(\frac {M}{V}\)I = \(\frac {Magnetic \, moment}{Volume}\) ➔ Unit of magnetic moment = Am^2; Unit of volume = m^3; I = \(\frac {Am^2}{m^3} = \frac {A}{m}\)

Thus, the units of magnetization and magnetic intensity is the same.

The correct choice is (b) Ferromagnetic materials

The EXPLANATION: The relative permeability of ferromagnetic materials is much LARGER than 1. Ferromagnetic substances are those, which when PLACED in a magnetic field are strongly magnetized in the DIRECTION of the magnetizing field, i.e., it is strongly attracted by a magnet.

Right option is (d) Maximum

To explain I WOULD SAY: Angle of dip is 90^o at geographical NORTH Pole because ATTRACTION on the North Pole of needle is very strong and the needle remains in vertical plane. At the magnetic equator, the needle will point horizontally, i.e. dip angle is 0^o. As you move from the magnetic equator towards the magnetic pole, the angle increases in the northern hemisphere. So, the angle of dip is maximum.

Correct choice is (a) Magnet exists as a monopole

For explanation I would say: Attractive property, directive property and the law of magnetic POLES are some of the important PROPERTIES of MAGNETS. So unlike electric charges, magnetic monopoles do not EXIST. EVERY magnet exists as a dipole.

The correct option is (B) North-south

The BEST explanation: When SUSPENDED freely, a thin long piece of magnet comes to rest NEARLY in the geographical north-south direction. When placed in a non-uniform MAGNETIC field, it tends to move from weaker to stronger magnetic field.

Correct OPTION is (c) χm = \(\frac {C}{T}\)

Best explanation: Curie’s law in magnetism states that the MAGNETIC susceptibility of paramagnetic MATERIALS is INVERSELY proportional to its absolute temperature and it is given by:

χm = \(\frac {C}{T}\)

Right option is (b) Electrical ORIGIN

Easy explanation: Magnetism is of electrical origin. The electrons revolving in an ATOM behave as tiny current loops and these current loops GIVE rise to magnetism. An electric current produces a magnetic field. This magnetic field can be visualized as a pattern of circular field LINES circling a wire.

The correct option is (c) There are abundant sources or SINKS of the MAGNETIC field inside a closed surface

Explanation: Gauss‘s law INDICATES that there are no sources or sinks of the magnetic field inside a closed surface. In other words, there are no FREE magnetic charges. HENCE, magnetic monopoles do not exist.

The correct OPTION is (d) μr > 1, χ > 0

The explanation is: The correct COMBINATION for paramagnetic substances is given as follows:

μr > 1, χ > 0

Paramagnetic materials have a SMALL and positive value of magnetic susceptibility (χ). The relative permeability (μr) of paramagnetic materials is just greater than 1.

The correct answer is (c) 3

To elaborate: THREE QUANTITIES are NEEDED to specify the magnetic field of the EARTH on its surface, namely, the HORIZONTAL component, the magnetic declination and the magnetic dip. These are known as elements of the earth’s magnetic field or magnetic elements.

Correct answer is (a) H = \(\frac {B_o}{\mu_o}\)

The best explanation: Magnetic INTENSITY in vacuum is defined as the ratio of APPLIED magnetic field (Bo) to the permeability of FREE space (μo). Magnetic intensity is denoted by H. The EXPRESSION is GIVEN by:

H = \(\frac {B_o}{\mu_o}\)

Right answer is (c) Paramagnetic materials

For explanation: Paramagnetic materials are those when suspended freely inside the magnetic FIELD, it slowly sets itself parallel to the direction of the magnetic field. When PLACED in a non-uniform magnetic field, it tends to MOVE from WEAKER to a stronger magnetic field.

Correct choice is (d) I = \(\FRAC {M}{V}\)

For explanation I would say: Intensity of magnetization is defined as the MAGNETIC moment developed per UNIT volume, when a magnetic SPECIMEN is subjected to the magnetizing field. Intensity of magnetization is denoted by I. The expression is given by:

I=\(\frac {M}{V}\)

Correct option is (B) Repulsion

The explanation: A MAGNET can attract another magnet or a MAGNETIC SUBSTANCE like iron. However, a magnet can repel another magnet only. So repulsion is the surer test of magnetism.

Right choice is (d) Am^2

The best EXPLANATION: The MAGNETIC dipole moment of a magnetic dipole is defined as the PRODUCT of its pole strength and magnetic length. The SI unit of magnetic dipole moment is ampere metre^2 (Am^2). Magnetic dipole moment is a vector quantity and is DIRECTED from south to north pole of the magnet.

Correct answer is (a) Vertical plane passing through the axis of a freely SUSPENDED or PIVOTED magnet

Best explanation: A vertical plane passing through the axis of a freely suspended or pivoted magnet is known as magnetic MERIDIAN of Earth. The vertical plane passing through the geographical North Pole and SOUTH Pole at a given place is known as the geographical meridian of that place.

Right choice is (b) False

To elaborate: Ferromagnetic materials do show hysteresis. When a ferromagnetic material is magnetized in one direction, it will not relax back to ZERO magnetization when the imposed MAGNETIZING field is removed. The phenomenon of hysteresis in ferromagnetic materials is the result of two EFFECTS ➔ rotation of magnetization and changes in size or NUMBER of magnetic DOMAINS.

Right OPTION is (c) It is the ratio of INTENSITY of magnetization to magnetic intensity

The best EXPLANATION: Magnetic susceptibility of a magnetic substance is defined as the ratio of the intensity of magnetization (I) to the magnetic intensity (H). The EXPRESSION is given by:

χm=\(\frac {I}{H}\)

Magnetic susceptibility measures the aptness of a magnetic substance to acquire MAGNETISM. It is a unit less constant of magnetic substance.

The correct choice is (C) 0.017

To explain: Given: χm1 = 0.0085; T1 = -80^0 C = -80 + 273 = 193 K; T2 = -180^0 C = -180 + 273 = 93 K

χm ∝ \(\frac {1}{T}\)

\(\frac {\chi_{m2}}{\chi_{m1}} \, = \, \frac {T_1}{T_2}\)

\(\frac {\chi_{m2}}{0.0085} \, = \, \frac {193}{93}\)

χm2 = \(\frac {193 \, \times \, 0.0085}{93}\)

χm2 = 0.017

Right answer is (d) tanδ=2tanλ

Best explanation: If a magnet is freely suspended or INCLINED or dipped, the angle between the horizontal and the angle of inclination of the magnet that is inclined only by the earth’s MAGNETIC field will indicate the magnetic LATITUDE. The relation is as FOLLOWS:

tanδ=2tanλ

Right choice is (b) 0.40 G

The best explanation: GIVEN: Horizontal COMPONENT (H) = 0.35 G; ANGLE of dip (δ) = 30^o

Required equation ➔ cosδ=\(\frac {H}{B}\)

B=\(\frac {H}{cos\delta } = \frac {0.35}{cos30^o} = \frac {0.35}{\frac {\sqrt {3}}{2}} =\frac {0.35\times 2}{1.732}\)=0.40

Therefore, the MAGNITUDE of the magnetic field at that PLACE is 0.40 G.

Right ANSWER is (d) Diamagnetic < PARAMAGNETIC < Ferromagnetic

For explanation I would say: Diamagnetic materials have a small and negative VALUE of magnetic SUSCEPTIBILITY. Paramagnetic materials have a small and positive value of magnetic susceptibility and ferromagnetic materials have a large and positive value of magnetic susceptibility.

The correct choice is (a) Not possible

The BEST EXPLANATION: No. The force on a charge is perpendicular to the DIRECTION of the magnetic FIELD at each point.

 F = q (v × B).

It is INAPPROPRIATE to call magnetic field lines as lines of force.

Right choice is (c) Zero

The explanation is: Gauss’s law indicates that there are no sources or sinks of the magnetic field INSIDE a closed surface. A “closed surface” is a surface that completely encloses a VOLUME with no holes. Therefore, the net magnetic FLUX through a closed surface is zero.

Right answer is (d) 499

For explanation I would say: Given: RELATIVE permeability (μr) = 500

Required EQUATION ➔ μr = 1+χm

χm = μr – 1

χm = 500 – 1

χm = 499

Therefore, the VALUE of MAGNETIC susceptibility is 499.

Right choice is (a) True

To explain: Soft IRON has high permeability and low retentivity and is used as an ELECTROMAGNET. The area under the hysteresis loop for soft iron is less. So where the repeated cycles of magnetization occur, there on USING soft iron core, energy losses are less. That is why soft iron is used in cores of transformers, galvanometers, GENERATORS, ETC.

Correct ANSWER is (b) ZERO

The best EXPLANATION: A bar magnet does not exert a force or torque on itself due to its field. But an ELEMENT of a current-carrying conductor experiences FORCES due to another element of the conductor. So, the torque exerted by a bar magnet on itself is zero.

Correct choice is (c) 155.8 J

Easiest EXPLANATION: Torque, τ = mBsin (θ).

Given: m = 20 J/T; B =9 T; θ = 60^o

τ = 20 JT^-1 × 9 T × sin(60^o)

τ = 155.8J.

Correct choice is (c) Magnetic intensity and intensity of magnetization are the same.

Easy explanation: The statement magnetic intensity and intensity of magnetization are the same is the FALSE one. They are not the same. When a MAGNET is entering a magnetic field, then the poles of the magnet EXPERIENCES certain forces. Magnetic intensity refers to the measure of these forces. But, the intensity of magnetization explains the change in the magnetic moment of a magnet as a function of volume. All the other statements are valid.

The correct answer is (b) FALSE

Easiest explanation: No, this statement is false. The EARTH ALWAYS has a vertical component except at the equator. Similarly, the earth always has a horizontal component except at the POLES.

The correct answer is (c) Magnetite

The best I can explain: Pieces of naturally occurring IRON ore, lodestone or magnetite had the PROPERTY of ATTRACTING small pieces of iron. Hence, magnetite is a natural MAGNET. All natural MAGNETS are permanent magnets, meaning they will never lose their magnetic power.

The correct option is (c) Copper

Easy explanation: A MAGNET is a MATERIAL that has both attractive and directive properties. It attracts small pieces of iron, nickel, COBALT, ETC. This PROPERTY of attraction is called magnetism. Going by this criteria, copper is not attracted by magnets.

Correct choice is (b) False

For explanation: No, aluminum is a paramagnetic MATERIAL. Paramagnetic materials are those, which when placed in a magnetic field are feebly magnetized in the DIRECTION of the magnetizing field, i.e. it is feebly ATTRACTED by a magnet.

Correct answer is (a) When the VERTICAL and HORIZONTAL components of earth’s magnetic FIELD are equal

The best I can explain: YES, the angle of dip at a place is equal to 45^o, when the vertical and horizontal components of earth’s magnetic field are equal. In this case ➔ δ=45^o

tanδ=\( \FRAC {B_V}{B_H}\)=1

So, BV=BH.

The CORRECT OPTION is (a) 2 Am^2

The best I can explain: Magnetic dipole MOMENT = POLE STRENGTH × Magnetic length.

Magnetic dipole moment = 20 Am × 0.1 m

Magnetic dipole moment = 2 Am^2.

Right option is (d) Zinc

The best explanation: Permanent magnets are made up of materials having HIGH retentivity, high coercivity, and high permeability such as steel. Other suitable materials for MAKING permanent magnets are alnico (an alloy of iron, ALUMINUM, nickel, COPPER, and cobalt), cobalt steel, and ticonal. That LEAVES zinc as the one that cannot be used to make permanent magnets.