Question

Two isolated point poles of strength $30A{m}^2$ and $60A{m}^2$ are placed at a distance of $0.3m$. The force of repulsion is:

• A. $2\times {10}^{-3}N$
• B. $2\times {10}^{-4}N$
• C. $2\times {10}^{5}N$
• D. $2\times {10}^{-5}N$

Answer 1

Answer: (A)

$2\times {10}^{-3}N$

Given : $m_1=30$ $A{m}^2$ $m_2=60$ $A{m}^2$ $r=0.3$ $m$

Force of repulsion : $F=\frac{{\mu }_o}{4\pi }\frac{m_1{m}_2}{r^2}$

$\therefore$ $F={10}^{-7}\times \frac{30\times 60}{(0.3{)}^2}=2\times {10}^{-3}$ $N$