Question

Two magnetic poles of pole strengths $324mA-m$ and $400mA-m$. are kept at a distance of $10cm$ in air. The null point will be at a distance of $\underset{–}{}$ ( in $cm$ ), on the line joining the two poles, from the weak pole if they are like poles :

• A. $4.73$
• B. $5$
• C. $6.2$
• D. $5.27$

Answer 1

The correct option is A $4.73$

$P_1=324\times {10}^{-3}Am$
$P_2=400\times {10}^{-3}Am$
$d^1=10cm$
$B^1=\frac{\mu 0P_1}{4\pi d^2}$
$B^2=\frac{\mu 0P_2}{4\pi {(10-d)}^2}$
$B_1=B_2$ at null point
$\frac{324\times {10}^{-3}}{d^2}=\frac{400\times {10}^{-3}}{(10-d/2)}$
$\frac{18}{d}=\frac{20}{10-d}$
$180=38d$
$d=4.73m$