• # question_answer 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 large from infinity to the third vertex is: A)  $U$                            B)  $2U$ C)  $3U$                          D)  $4U$

As, potential energy of the system when there is two changes is $Ui=U.$ Now, when these are three charges situated of the three corners is                                 ${{U}_{f}}=U$                 $\therefore$  ${{U}_{l}}={{U}_{f}}-{{U}_{i}}=3U-U=2U$ $=2U$    (in magnitude)