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?

As part of your daily workout, you lie on your back and push with your feet against a platform attached to two stiff springs arranged side by side so that they are parallel to each other. when you push the platform, you compress the springs. you do an amount of work of 79.0 j when you compress the springs a distance of 0.230 m from their uncompressed length. (a) what magnitude of force must you apply to hold the platform in this position? (b)how much additional work must you do to move the platform a distance 0.230 m farther? (c) what maximum force must you apply to move the platform a distance 0.230 m farther?