Question

Two identical charges are placed at the two corners of an equilateral triangle. The potential energy of the system is U. The work done in bringing an identical charge from infinity to the third vertex is-

• A. U
• B. 2U
• C. 3U
• D. 4U

Answer 1

Answer: (B)

2U

Answer 2

U_i = $\frac { \mathrm { kq } ^ { 2 } } { \mathrm { a } }$ = U

U_f = $\frac { 3 \mathrm { kq } ^ { 2 } } { \mathrm { a } }$ = 3U

W = U_f – U_i = 3U – U = 2U