Question

A point charge +Q is placed at point O as shown in the figure. Is the potential difference $V_A-V_B$ positive, negative or zero?

Answer 1

The potential at a point,

$V=\frac{kq}{r}$

For a charge Q, $V_A-V_B=kQ(\frac{1}{r_A}-\frac{1}{r_B})$

where $r_A<r_B$

So, $\frac{1}{r_A}>\frac{1}{r_B}$

So, $(\frac{1}{r_A}-\frac{1}{r_B})>0$

Since Q is positive. So, $V_A-V_B$ is also positive.