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The strength of the magnetic field at a point due to current carrying wire depends on:

• the current in the wire 
• distance of the point from 
• the wire the orientation of 
• the point from the wire and the magnetic nature of the medium.

Correct answer is (C) both a force and a torque

(d) Am²
Unit of magnetic moment is Am²

The magnetic induction left behind in the sample after the magnetising field has been removed is called residual magnetism or rententity.

(b) N

Wb × \(\frac{{A}}{{m}}\) is equal to N.

The vertical plane passing through the magnetic axis of a freely suspended small magnet is called magnetic meridian. The earth’s magnetic field acts in the direction of the magnetic meridian.

(c) static charge
Magnetic field does not interact with static charges.

(i) CuCl₂ (ii) Oxygen.

Potential Energy of a Magnetic Dipole
As τ = MB sinθ
If the dipole is rotated against the action of this torque, work has to be done. This work is stored as potential energy of the dipole.
The work done in turning the dipole through a small angle dθ is
dW = τdθ = MB sinθdθ
If the dipole is rotated from an initial position θ = θ₁ to the final position θ = θ₂, then the total work done will be
W = \(\int d W=\int_{\theta_{1}}^{\theta_{2}} M B \sin \theta d \theta=-M B[-\cos \theta]_{\theta_{1}}^{\theta_{2}}\)
= -MB(cosθ₂ – cosθ₁)
This work done is stored as the potential energy U of the dipole.
∴ U = -MB(cosθ₂ – cosθ₁)
The potential energy of the dipole is zero when
\(\vec{M} \perp \vec{B}\). So the potential energy of the dipole in any orientation θ can be obtained by putting θ₁ = 90° and θ₂ = θ in the above equation.
∴ U = -MB(cosθ – cos 90°)
or U = -MBcosθ = -M. B

Neutral point is the point where the magnetic field due to magnet is equal and opposite to the horizontal component of earth’s magnetic field. The resultant magnetic field at the neutral point is zero. In this way two neutral points are obtained.

On placing the north pole or south pole of bar magnet downwards in vertical position, we found out only one neutral point whose position is from north pole to south or south towards north.

When suspended freely in a magnetic field:

1. the paramagnetic rod sets itself parallel to the field, and

2. the diamagnetic rod itself perpendicular to the field.

(a) orbital motion of electrons
Due to orbital motion of electrons.

(b) zero
Magnetic moment of diamagnetic substance is zero.

Correct answer is (D) are in the direction from S pole to N pole

Correct answer is (D) one of the geomagnetic poles

One of the reason for the fact is that, when a material has µ_r > > 1, the field lines meet the material nearly normally.

Yes, a paramagnetic sample with saturated magnetisation will have the same order of magnetisation as the magnetisation of a ferromagnetic substance. However, the saturated magnetisation will require magnetising field too high to achive. Further, there may be a minor difference in the strengths of the atomic dipoles of paramagnetic and ferromagnetic materials.

(a) attract each other

i. Axis: It is the line passing through both the poles of a bar magnet. There is only one axis for a given bar magnet.

ii. Equator:

• A line passing through the centre of a magnet and perpendicular to its axis is called magnetic equator.
• The plane containing all equators is called the equatorial plane.
• The locus of points, on the equatorial plane, which are equidistant from the centre of the magnet is called the equatorial circle.
• The popularly known ‘equator’ of the planet is actually an ‘equatorial circle’. Such a circle with any diameter is an equator.

iii. Magnetic length (2l)

It is the distance between the two poles of a magnet.

Magnetic length (2l) = \(\frac{5}{6}\) × Geometric length.

Angle between the geographic and the magnetic meridian at a place is called magnetic declination (α).

Magnetic elements of the Earth (B_H, α and ø) vary from place to place and also with time. The maps providing these values at different locations are called magnetic maps.

Angle of declination: The angle between the geographical meridian and the magnetic meridian at a place is called the magnetic declination at that place.

Angle of dip: The angle made by the earth’s total magnetic field \(\vec B\) with the horizontal direction in
the magnetic meridian is called angle of dip (δ) at any place.