Question

Two point charges with Q1 = 8uC and Q2 = -4uC are arranged as shown in the figure. If L = 0.03 m, what is the electric field at the origin?

Answer 1

$$E=k\frac{q_1}{L^2}-k\frac{q_2}{L^2}\\E=9\cdot10^9\frac{8\cdot10^{-6}}{0.03^2}-9\cdot10^9\frac{-4\cdot10^{-6}}{0.03^2}=1.2\cdot10^8\frac{V}{m}$$