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Question
Let r be the distance of a point on the axis of a bar magnet from its centre. The magnetic field at such a point is proportional to
Options
`1/r`
`1/r^2`
`1/r^3`
none of these
Solution
None of these
Magnetic field B due to a bar magnet of magnetic moment M at distance r of the point on the axis of the magnet from its centre is given by
`B = (u_0)/(4pi) (2Mr)/(r^2 - l^2)^2`
Here, 2l is the length of the magnet.
So, from the above formula, it can be easily seen that `B ∝ r/(r^2 - l^2)^2`
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