Question

What is the magnitude of a point charge due to which the electric field $30cm$ away has the magnitude $2Newton/coulomb$ ? $[1/4\pi \epsilon 0=9\times {10}^{9}N{m}^2]$

• A. $2\times {10}^{-11}coulomb$
• B. $3\times {10}^{11}coulomb$
• C. $5\times {10}^{11}coulomb$
• D. $9\times {10}^{11}coulomb$

Answer 1

The correct option is A $2\times {10}^{-11}coulomb$

Electrric field due to apoint charge at a distance x from it.

$\begin{array}{c}=\frac{1}{4}e\frac{q}{x^2}\\ 2=8.9\times {10}^9\times \frac{q}{{\left(0.30\right)}^2}\\ q=2\times \frac{0.09}{8.9}\times {10}^{-9}\\ =2.02\times {10}^{-11}C\end{array}$

Hence, Option $A$ is correct .