Question

The pole strength of $12$cm long bar magnet is $20$ A m having Magnetic moment $20\times 0.12A{m}^2$.The magnetic induction at a point $10$cm away from the centre of the magnet on its axial line is $[\frac{{\mu }_0}{4\pi }={10}^{-7}H{m}^{-1}]$

• A. $1.17\times {10}^{-3}$ T
• B. $2.20\times {10}^{-3}$ T
• C. $1.17\times {10}^{-2}$ T
• D. $2.20\times {10}^{-2}$ T

Answer 1

Answer: (A)

$1.17\times {10}^{-3}$ T

On axial line, $B=\frac{{\mu }_0}{4\pi }\frac{2md}{(d^2-l^2{)}^2}$

Given, $2l=12cm=0.12m$

Pole strength = $20Am,d=10cm=0.1m$

Magnetic moment m = $20\times 0.12A{m}^2$

$\therefore B={10}^{-7}\times \frac{2\left(20\right)\times \left(0.12\right)\times 0.1}{\left[\right(0.1{)}^2-(0.06{)}^2{]}^2}=1.17\times {10}^{-3}T$