Question

Two point charges $+q$ and $-q$ are located at points $(0,0,-a)$ and $(0,0,a)$ respectively. The potential at a point $(0,0,z)$ where $z>a$ is

• A. $\frac{2qa}{4\pi {ϵ}_0(z^2+a^2)}$
• B. $\frac{q}{4\pi {ϵ}_{0}a}$
• C. $\frac{qa}{4\pi {ϵ}_0{z}^2}$
• D. $\frac{2qa}{4\pi {ϵ}_0(z^2-a^2)}$

Answer 1

The correct option is D $\frac{2qa}{4\pi {ϵ}_0(z^2-a^2)}$

$V=V_1+V_2$

$⟹V=\frac{q}{4\pi {ϵ}_o(z+a)}-\frac{q}{4\pi {ϵ}_o(z-a)}$

$⟹V=\frac{2qa}{4\pi {ϵ}_o(z^2-a^2)}$

Answer-(D)