Electrostatics
Intermediate
Electric Field
Source: High school physics (Chinese)
Problem Sets:
Electrostatics
Problem
A point charge $Q$ is placed in air. The electric field strength at a distance of 0.2 m from $Q$ is 0.5 N/C.
Find the magnitude of the charge $Q$.
$|Q| = 2.2 \times 10^{-12}$ C
The electric field $E$ from a point charge $Q$ at a distance $r$ is given by $E = k \frac{|Q|}{r^2}$. We can rearrange this formula to solve for the magnitude of the charge, $|Q|$.
$$|Q| = \frac{E r^2}{k}$$