Question

A +200μC is place at the origin and a -300μC is placed on 1m to the right of it. What is the magnitude and direction of the electric field midway between the 2 charges and 30 cm to the right of the negative charge?

Answer 1

The net field

$$E=E_1+E_2=k\frac{|q_1|}{r_1^2}+k\frac{|q_2|}{r_2^2}$$

$$E=9*10^9\left(\frac{200*10^{-6}}{0.5^2}+\frac{300*10^{-6}}{0.5^2}\right)\\ =1.8*10^7\:\rm N/C$$