Four point charges are placed at the corners of a square. Each charge has the identical value Q. The length of the diagonal of the square is 2a. Find out the total electric field at the center of the square. Please give your answer in terms of coulomb constant k, Q and a. Required:
a. What is the total electric field at the center of the square?
b. What is the total potential at the center of the square?

I'm thinking it's 2 you are asked to explain the earth's magnetic field. which is the best reply? 1. the earth's magnetic south is similar to the north pole of a magnet. 2. the earth's core has a strong magnetic charge similar to the south pole of a magnet. 3. the earth's geomagnetic south is similar to the south pole of a magnet. 4. the earth's magnetic charge is not centered at either pole; it varies based on location.