Question

An electric dipole of length 2 cm is placed with its axis making an angle of 30ŗ to a uniform electric field 10⁵ N/C. If it experiences a torque of 10$\sqrt{3}$ Nm, then potential energy of dipole–

• A. –10 J
• B. –20 J
• C. –30 J
• D. – 40 J

Answer 1

Answer: (C)

–30 J

Answer 2

t = PE sin 30

10 $\sqrt { 3 }$ = $\frac { \mathrm { PE } } { 2 }$

PE = 20 $\sqrt { 3 }$

Potential Energy = –PE cos 30

\ Potential energy = –20 $\sqrt { 3 }$ × $\frac { \sqrt { 3 } } { 2 }$

= – 10 × 3 = –30 J