Physics Class 12 NCERT Solutions: Chapter 5 Magnetism and Matter Part 5

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Dipole magnetic field and electric field

Dipole Magnetic Field and Electric Field

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Q: 14. If the bar magnet in exercise (Reference: Chapter 5 Magnetism And Matter Part 4) is turned around by, where will the new null points be located?

Answer:

The magnetic field on the axis of the magnet at a distance, can be written as:

Where,

Magnetic moment

Permeability of free space

Horizontal component of the magnetic field at

If the bar magnet is turned through , then the neutral point will lie on the equatorial line.

Hence, the magnetic field at a distance , on the equatorial line of the magnet can be written as:

Equating equations (1) and (2), we get:

The new null points will be located on the normal bisector.

Q: 15. A short bar magnet of magnetic moment is placed with its axis perpendicular to the earth’s field direction. At what distance from the centre of the magnet, the resultant field is inclined at with earth’s field on s

(A) Its normal bisector and (b) its axis. Magnitude of the earth’s field at the place is given to be. Ignore the length of the magnet in comparison to the distances involved.

Answer:

Magnetic moment of the bar magnet,

Magnitude of earth’s magnetic field at a place,

(A) The magnetic field at a distance R from the centre of the magnet on the normal bisector is given by the relation:

Where,

Permeability of free space

When the resultant field is inclined at with earth’s field,

(B) The magnetic field at a distanced from the centre of the magnet on its axis is given as:

The resultant field is inclined at with earth’s field.