physics
posted by jude .
Given a square of sidelength a = 5 cm. We place a charged particle at each corner, three of them carry + 2 nC of charge and one carries the same amount of negative charge.
What is the magnitude of the electric field at the center of the square?
I don't know how to start this problem and would really appreciate it if someone could tell me the method.
Thank you

The center of the square is 5/sqrt2 = 3.535 cm from each corner. The fields due to the two +2nC charges at opposite corners will cancel out. The other two opposite charges will add, and the field will act along the diagonal between them.
Calculate the E field due to the negative charge using Coulomb's Law, and double it to account for the positive charge at the opposite corner. 
Is the point charge considered to have a charge of 1?