Question

Two charges $5\mu C$ and $-20\mu C$ are placed 30 cm apart. Find the strength of electric field at the mid point between them.

Answer 1

Let "O" be the midpoint between the charges $Q_{1}and{Q}_2$.
The strength of electric field at the point 'O' due to $Q_1$ is.
$E_1=\frac{1}{4\pi {ϵ}_0}\frac{Q_1}{d_1^2}$
$=9\times {10}^9\times \frac{5\times {10}^{-6}}{(0.15{)}^2}$
$=2\times {10}^{6}N$
The strength of electric field at the point 'O' due to $Q_1$ is,
$E_2=\frac{1}{4\pi {ϵ}_0}\frac{Q_2}{d_2^2}=9\times {10}^9\times \frac{20\times {10}^{-6}}{(0.15{)}^2}$
$=8\times {10}^{6}N$
Total strength of electric field at the point 'O' s $E=E_1+E_2$
$=2\times {10}^6+8\times {10}^6=[2+8]{10}^6={10}^{7}N$