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Question
A deflection magnetometer is placed with its arms in north-south direction. How and where should a short magnet having M/BH = 40 A m2 T−1 be placed so that the needle can stay in any position?
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Solution
Given :
Ratio , `M/B_H = 40 "Am"^2"/"T`
Since the magnet is short, l can be neglected.
So, using the formula for `M/B_H` from the magnetometer theory and substituting all values, we get
`M/B_H = (4pi)/(u_0) (d^3)/2 = 40`
⇒ `d^3 = 40 xx 10^-7 xx 2`
⇒ `d^3 = 8 xx 10^-6`
⇒ `d = 2 xx 10^-2 "m" = 2 "cm"`
Thus, the magnet should be placed in such a way that its north pole points towards the south and it is 2 cm away from the needle.
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