question_answer

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 \[11.3{}^\circ \] with the axis of the Earth. At Mumbai, declination is nearly zero. Then.                                                                                                                           (NCERT EXEMPLAR)

A) the declination varies between \[11.3{}^\circ W\] to \[11.3{}^\circ E\].

B)             the least declination is \[0{}^\circ \].

C)             the plane defined by dipole axis and the Earth axis passes through Greenwich.

D)             declination averaged over the Earth must be always negative.

Correct Answer: A

Solution :

(a) the declination varies between \[11.3{}^\circ W\] to \[11.3{}^\circ E\]. Since the axis of the magnetic dipole placed at the centre of Earth makes an angle of \[11.3{}^\circ \] with the axis of Earth, the two possibilities arise as shown in above figure. Hence, the declination varies between \[11.3{}^\circ W\] to \[11.3{}^\circ E.\]