Three equal-magnitude point charges of varying signs are placed at three of the corners of a square of side d as shown in the figure. Which one of the arrows shown represents the direction of the net electric field at the vacant corner of the square?
A) A
B) B
C) C
D) D

Question

Three equal-magnitude point charges of varying signs are placed at three of the corners of a square of side d as shown in the figure. Which one of the arrows shown represents the direction of the net electric field at the vacant corner of the square? 
A) A 
B) B 
C) C 
D) D

Quizplus · Accepted Answer

By symmetry, the electric field vectors pointing towards the two negative charges cancel out, leaving only the electric field vectors pointing towards the positive charge. Therefore, the net electric field at the vacant corner is directed towards the positive charge, which is represented by arrow B.

Three Equal-Magnitude Point Charges of Varying Signs Are Placed at Three