The distance of two points on the axis of a magnet from its center are 10cm . The ratio of magnetic field at these points is 12.5:1. The length of the magnet is :
A
5cm
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B
25cm
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C
10cm
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D
20cm
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Solution
The correct option is C10cm
magnetic intensity on the axis of a magnet from its centre at a distance r
B=μ02rM4π(r2−L2)2
The ratio of magnetic intensity on the axis at a distance r1 and r2 is B1 and B2