Question

A short bar magnet is placed with its north pole pointing north. The neutral point is 10 cm away from the centrecof the magnet. if H=0.4G, calculate the magnetic monent of the magnet???

Answer 1

Magnetic field due to the bar magnet

H = m4πd^2
where d is the point at which net magnetic field is zero.(due to earth and the bar magnet)
d = 10 cm = 0.1 mH = 0.4 gauss =0.4×10^−4T on substituting the value m = 5×10−6 Am^2

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Answer 2

when north pole of the magnet points toeards magnetic north, null point is obtained on perpendicular bisector of the magnet.simultaneously magnetic field due to the bar magnet should be equal to the horizontal component of the earth magnetic field H.

Thus,


M=(0.4×10^-4)(10×10^-2)^3/10^-7
=0.4A-m^2
.
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