Q. 1 E

Answer the following question regarding earth’s magnetism:

The earth’s field, it is claimed, roughly approximates the field due to a dipole of magnetic moment 8 × 1022 J T–1 located at its centre. Check the order of magnitude of this number in some way.

Answer :


Magnetic moment, m = 8 × 1022 JT-1

Radius of earth, r = 6.4 × 106m

Our task is to check the order of m, we shall attempt to do so by finding the magnetic field of earth using the available information. If we are close to the standard measured value then the order of m is correct.

We know that magnetic field strength,


Where, �0 = permeability of free space

0 = 4π × 10-7 TmA-1

m = magnetic moment

r = radius

Putting values in equation (1) we get,

B = 0.3 × 10-4T

B = 0.3 G

Which is a close value to the strength of earth’s magnetic field. Hence the order of magnetic moment is correct.

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