Question

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

• 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, $B=\frac{{\mu }_o}{4\pi }\frac{2md}{(d^2-l^2{)}^2}$
Given, $2l=12$cm $=0.12$m
Pole strength $=20$A m, d$=10$cm $=0.1$m
Magnetic moment m $=20\times 0.12$A $m^2$
$\therefore B={10}^{-7}\times \frac{2\left(20\right)\times \left(0.12\right)\times 0.1}{\left[\right(0.1{)}^2-(0.06{)}^2{]}^2}=1.17\times {10}^{-3}T$