# Why is $E_1=\frac{F}{q}=\frac{K\frac{Q_1 Q_2}{x^2}}{Q_2}$, instead of $=\frac{K\frac{Q_1 Q_2}{x^2}}{Q_1}$?

I have a question about these electric field strength formulas

Why is $$\E_1=\frac{F}{q}=\frac{K\frac{Q_1 Q_2}{x^2}}{Q_2}\$$, instead of $$\=\frac{K\frac{Q_1 Q_2}{x^2}}{Q_1}\$$?

$$\K\$$ is constant $$\=9 \times 10^9\$$

• Where did the formulas come from specifically? – Andy aka Apr 10 at 12:16
• Please do something about the title text, it's a mess. – Wossname Apr 10 at 12:37

I am also not 100% sure what is denoted by E_1. If it is the electric field at P due only to Q_1, than $$E_1 = \frac 1 {4 \pi \epsilon_0} \frac {Q_1 Q_2} {x^2}$$. If you should consider the effect of Q_2, just use superposition.