Question

Two charges $+3.2 \times 10^{-19} C$ and $-3.2 \times 10^{-19} C$ kept $2.4\, \mathring{A}$ apart form a dipole. If it is kept in uniform electric field of intensity $4 \times 10^{5} volt / m$, then what will be its electrical energy in equilibrium?

• A. $+3 \times 10^{-23} J$
• B. $-3 \times 10^{-23} J$
• C. $-6 \times 10^{-23} J$
• D. $-2 \times 10^{-23} J$

Answer 1

Answer: (B)

Potential energy of electric dipole
$U=-p E \cos \theta=-(q \times 2 l) E \cos \theta$
$U=-\left(3.2 \times 10^{-19} \times 2.4 \times 10^{-10}\right) 4 \times 10^{5} \cos \theta$
$U=-3 \times 10^{-23} J$ (approx.)