Question

The magnetic field of the earth can be modelled by that of a point dipole placed at the centre of the earth. The dipole axis makes an angle of 11.3° with the axis of the earth. At Mumbai, declination is nearly zero. Then, ______.

Options

• the declination varies between 11.3° W to 11.3° E.

• the least declination is 0°.

• the plane defined by dipole axis and the earth axis passes through Greenwich.

• declination averaged over the earth must be always negative.

Answer 1

The magnetic field of the earth can be modelled by that of a point dipole placed at the centre of the earth. The dipole axis makes an angle of 11.3° with the axis of the earth. At Mumbai, declination is nearly zero. Then, the declination varies between 11.3° W to 11.3° E.

Explanation:

The magnetic field lines of the earth resemble that of a hypothetical magnetic dipole located at the centre of the earth.

The axis of the dipole does not coincide with the axis of rotation of the earth and it is tilted at some angle (angle of declination). Here in this situation, the angle of declination is approximately 11.3° with respect to the later. Here two possibilities arise as shown in the figure below.