Question

______ is that charge which repels an equal and similar charge with a force of $9\times {10}^{9}N$, when placed in vacuum at a distance of $1m$ from it.

• A. One coulomb
• B. Two coulomb
• C. Three coulomb
• D. Four coulomb

Answer 1

The correct option is A One coulomb

we know that force is given by $F=\frac{Q_1{Q}_2}{4\pi {ϵ}_o{R}^2}$

Now, here $Q_1=Q_2=Q$ and

$R=1m$ and $F=9\times {10}^{9}N$

And, $\frac{1}{4\pi {ϵ}_o}=9\times {10}^9$

Hence from force equation-

$⟹\frac{9\times {10}^9\times Q^2}{1^2}=9\times {10}^9$

$⟹Q^2=1$

$\implies Q=\pm1C$

Hence charge is $1coulomb$.

Answer-(A)