# A bar magnet of magnetic moment 2A-m2 is kept such that its north pole faces the earth's geographical east and its west faces the geographical west. If the horizontal component of earth's magnetic field is 20 microtesla, find the position of neutral point.

23 Points
14 years ago

Dear Hinan,

Bh= (μ0/4π)*M*(3cos2 θ -1)/l3

 B is the magnetic field, in teslas, at any point in space that isn't at the origin. It is equal to the sum of two field components, BX the magnetic field component which is aligned with the x axis and Br the magnetic field component which is in a radial direction. x is the distance, on axis, from the dipole to the field measurement point, in meters. l is the distance from the dipole to the field measurement point, in meters. q is angle between the dipole axis, and the position vector of the field measurement point.

Given that horizontal component of the field is 20 micro tesla and we know the dip of the earths magnetic field as 11.50 thus tan 11.50 = Bearth horizontal/Bearth vertical

• ð Bearth vertical = 98.303 micro tesla
• ð And the neutral point will be observed on the axis of the dipole which implies θ = 0 and thus

20*10^-6 tesla =  10^-7 * 2*2/ l3

• ð L = 0.271 m
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