CBSE Class 12 Physics Notes Chapter 5 - Magnetism and Matter

What Happens to the Dipole Moment of a Magnet?

When a magnet is experiencing a dipole moment m, and it is placed in a uniform magnetic field B, then it experiences:

  • The force on it as zero
  • The torque on it as m*B
  • The potential energy can be said to be as -m*B. Where the zero of energy is determined when m is perpendicular to B

For more information on Magnetic Field and Magnetic Field Lines, watch the below video

Gauss’ Law for Magnetism

Gauss’ law of magnetism points out the fact that the net magnetic flux through any surface which is closed tends to be zero.

Components of the Earth’s Magnetic Field

Three components have to be taken care of in order to particularise the earth’s magnetic field:

  • The horizontal component
  • Magnetic Dip
  • Magnetic Declination

How Are Magnetic Materials Classified?

Magnetic Materials are classified into three types:

  • Diamagnetic – whose χ (magnetic sensitivity of the material) is having negative value and small
  • Paramagnetic – for this, the χ is positive and small
  • Ferromagnetic – for this material, the χ is large

Permanent Magnets

When substances are exposed to room temperature, they retain their ferromagnetic properties for a longer time and are called permanent magnets.

Students can refer to the short notes and MCQ questions along with separate solution pdf of this chapter for quick revision from the links below:

To know more about magnetism and magnetic field, keep visiting BYJU’S website.

Important Questions

  1. Answer the following questions regarding Earth’s magnetism:
    1. With the specification of the Earth’s magnetic field, name the independent quantities.
    2. In southern India, If the angle of dip at a location is about 30°, do we expect a greater or smaller dip angle in Britain?
    3. If we made a map of magnetic field lines at New Delhi, would the lines come out of the ground or go into the ground?
    4. In which direction would a compass be free to move in the vertical plane point if the compass is located right on the geomagnetic north or south pole?
    5. Check the order of magnitude of the earth’s field if the dipole of the magnetic moment is 20 × 1022 J T–1 and is located at its centre.

Related Topics:

Important Questions on Magnetism and Matter

NCERT Solutions for Magnetism and Matter

NCERT Exemplars for Magnetism and Matter

Magnetism and Matter

Frequently Asked Questions on Magnetism and Matter


As we go from the magnetic equator towards the geographical south pole, what will be the angle of the dip?

As we move from the equator to the geographical south pole (which is near the magnetic north pole), the vertical component of the Earth’s magnetic field increases, and hence, the angle of dip goes on increasing. At the two magnetic poles, the magnetic needle rests vertically, such that the angle of dip at the two poles is 900. On the magnetic equator, the magnetic needle rests horizontally, such that the angle of dip is 00.


A magnetising field of 5000 A/m produces a magnetic flux of 5 × 10−5 wb in an iron rod is 0.5 cm2, then what is the permeability of the rod?

The permeability of the rod will be 2 × 10−4 H/m.


The poles of a horse-shoe magnet, each of pole strength 2 Am, are at 4 cm apart. What is the magnetic moment of the horse-shoe magnet?

The magnetic moment of the horse-shoe magnet is 0.08 Am2.


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