Question

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

• 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)

On axial line, $B=\frac{{\mu }_0}{4\pi }\frac{2md}{{\left(d^2-l^2\right)}^2}$
Given, $2l=12cm=0.12m$
Pole strength $=20Am$, $d=10cm=0.1m$
Magnetic moment $m=20\times 0.12A{m}^2$
$\therefore B=10^{-7}\times \frac{2\left(20\right)\times \left(0.12\right)\times 0.1}{{\left[{\left(0.1\right)}^2-{\left(0.06\right)}^2\right]}^2}=1.17\times 10^{-3}T$