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A bar magnet is 10 cm long kept with i...

A bar magnet is 10 cm long kept with its north pole pointing north. A neutral point is formed at a distance 15cm from each pole. given the horizontal component of earth field to be 0.4 gauss the pole strength of the magnet is

A

9A-m

B

6.75 A-m

C

27 A-m

D

1.35 A-m

Text Solution

Verified by Experts

The correct Answer is:
D
Length of magnet =`10 cm =10xx10^(-2)m`
`r=15xx10^(-2)m`
`OP=sqrt(225-25)=sqrt(200)cm`
since at the neutral point magnetic field due to the magnet equal to `B_(H`

`B_(H)=(mu_(0))/(4pi).(M)/(OP^(2)+AO^(2))^(3//2)`
`(0.4xx10^(-4))/(10^(-7))xx225xx10^(-4^(3//2))=M`
`0.4xx10^(3)xx10^(-6)=M`
`M=1.35 A-m`
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