Question

An electric dipole, of length $2 \, cm$ , is placed with its axis making an angle $30^\circ $ with a uniform electric field. If it experiences a torque of $10\sqrt{3} \, N \, m$ , then potential energy of the dipole is

• A. $-10 \, J$
• B. $-20 \, J$
• C. $-30 \, J$
• D. $- \, 40 \, J$

Answer 1

Answer: (C)

$\tau \, = \, PE \, sin \, 30$
$10\sqrt{3} \, = \, \frac{P E}{2}$
$PE \, = \, 20\sqrt{3}$
Potential energy = $-PE \, cos \, 30$
potential energy = $-20\sqrt{3} \, \times \, \frac{\sqrt{3}}{2}$
$= \, - \, 10 \, \times \, 3 \, = \, -30 \, J$