Question

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 ${11.3}^0$ with the axis of Earth. At Mumbai, declination is nearly zero. Then,

• A. the plane defined by dipole axis and Earth axis passes through Greenwich
  
  
  
• B. the least declination is $0^{\circ }$
  
  
• C. Declination averged over Earth must be always negative.
• D. the declination varies between ${11.3}^{\circ }W\text{to}{11.3}^{\circ }E$
  
  
  

Answer 1

The correct option is D the declination varies between ${11.3}^{\circ }W\text{to}{11.3}^{\circ }E$

The magnetic field of the earth represented as below:



The magnetic field of the earth represented as below:

The earth is taken as a dipole at the centre. The axis of the dipole does not coincide with the axis of rotation of the earth. It makes an angle of ${11.3}^{\circ }$ with the axis of the earth. Now as the angle of declination in Mumbai is nearly zero, hence, the difference between the angles is equal to ${11.3}^{\circ }$ from the axis of the earth either in west or in east.

Final Answer: (a)