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 $\left[\frac{\mu_{0}}{4\pi} = 10^{-7}\,H\,m^{-1}\right]$

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