physics
posted by amber .
Four point charges have the same magnitude of 2.62 1012 C and are fixed to the corners of a square that is 3.80 cm on a side. Three of the charges are positive and one is negative. Determine the magnitude of the net electric field that exists at the center of the square.

Symettry. Two opposite charges must be +, so they cancel E since opposite directions. tHe other two add, so E=k2q/distance^2
where distance is 0ne half of the diagonal.