A bar magnet is cut into two equal halves by a plane...

A bar magnet is cut into two equal halves by a plane parallel to the magnetic axis. Of the following physical quantities, the one which remains unchanged is.
(a) pole strength
(b) magnetic moment
(c) intensity of magnetisation
(d) moment of inertia

Key Concepts

Intensity of Magnetisation

Intensity of magnetisation is an intrinsic property of a magnetic material defined as the magnetic moment per unit volume. Since it depends on the alignment of magnetic domains within the material, this quantity remains unchanged when the material is physically divided, provided that the internal microstructure and the state of magnetisation of each resulting part remain uniform.

Moment of Inertia

The moment of inertia is a measure of an object's resistance to rotational acceleration about an axis and depends on the mass distribution relative to that axis. It is a mechanical property that changes if the mass or its distribution is altered, such as when a magnet is divided into parts.

Pole Strength

Pole strength is an idealized concept representing the equivalent magnetic charge at the ends of a bar magnet. It is used to quantify the strength of a magnet's poles. Although cutting a magnet may reduce the total pole strength of a piece (as the magnet is divided into smaller sections), pole strength is dependent on the amount of magnetic material and its configuration.

Magnetic Moment

The magnetic moment is a vector quantity that describes both the strength and the orientation of a magnetic source. It is proportional to the product of the pole strength and the distance between the poles. When a magnet is physically divided, the magnetic moment of each piece may change because both the effective pole strengths and the pole separation may be altered.

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