An even number ofn identical negative point charges-q are placed at equally spaced intervals on a circular plastic ring of radius a, such that each charge -q has an identical charge -q 180° opposite to it. (a) Derive an expression for the electric potential Vat point Pa distance z above the center of the ring. Your answer must be in terms ofk, q, a, and z. (b) Derive an expression for the E-field at P. Again, your answer must be in terms of k, q, a, and z. I.

An even number ofn identical negative point charges-q are placed at equally spaced intervals on a circular plastic ring of radius a, such that each charge -q has an identical charge -q 180° opposite to it. (a) Derive an expression for the electric potential Vat point Pa distance z above the center of the ring. Your answer must be in terms ofk, q, a, and z. (b) Derive an expression for the E-field at P. Again, your answer must be in terms of k, q, a, and z. I.