Question

A point charge produces an electric field of magnitude 5.0 $N{C}^{-1}$ at a distance of 40 cm from it. What is the magnitude of charge?

• A. $8.9\text{C}$
• B. $8.9\times {10}^{-11}\text{C}$
• C. $-8.9\times {10}^{11}\text{C}$
• D. ${10}^{-11}\text{C}$

Answer 1

The correct option is B

$8.9\times {10}^{-11}\text{C}$

All you need to know is the expression for electric field in terms of the charge and distance from it!

Here E = 5.0 $N{C}^{-1}$ as given

Distance given is 40 cm = 0.4 m

We know $|\overrightarrow{E}|=\frac{1}{4\pi {\epsilon }_0}\frac{Q}{r^2}$

So $5.0=9\times {10}^9\times \frac{Q}{(0.4{)}^2}\Rightarrow Q=8.9\times {10}^{-11}C$