Four equal charges of magnitude q are placed in the corners of a square whose side has length l. the permittivity of vacuum is denoted as €0. (1) what is the electric field at the center of the square? (2) what is the electric potential at the center of the square? here, the electric potential at infinity is defined to be zero. (3) let us assume a charge of magnitude q' is brought from infinity to the center of the square. what is the change in the potential energy of this charge? (4) how much work must be done by an outside force to bring in this charge?