일반물리학 2 — Electric Fields: Problem 25

25 The nucleus of a gold-197 atom contains 79 protons. Assume that the nucleus is a sphere with radius 6.98 fm and with the charge of the protons uniformly spread through the sphere. At the surface of the nucleus, what are the (a) magnitude and (b) direction (radially inward or outward) of the electric field produced by the protons?