Question: Q. 1. The magnetic field of Earth can be modelled by that of a point dipole placed at the centre of the Earth. The dipole axis makes an angle of $11.3^{\circ}$ with the axis of Earth. At Mumbai, declination is nearly zero. Then,
(a) the declination varies between $11.3^{\circ} \mathrm{W}$ to $11.3^{\circ} \mathrm{E}$.
(b) the least declination is $0^{\circ}$.
(c) the plane defined by dipole axis and Earth axis passes through Greenwich.
(d) declination averaged over Earth must be always negative.
[NCERT Exemplar]
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Solution:
Ans. Correct option : (a)
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 tiled at ome angle (angle of declination).
In this situation, the angle of declination is approximately $11.3^{\circ}$ with respect to the later. So, there is two possibilities arisesas shown :
So that the declination varies between $11.3^{\circ} \mathrm{W}$ to $11.3^{\circ} \mathrm{E}$.
