An early model of the atom, proposed by rutherford after his discovery of the atomic nucleus, had a positive point charge +ze (the nucleus) at the center of a sphere of radius r with uniformly distributed negative charge −ze. z is the atomic number, the number of protons in the nucleus and the number of electrons in the negative sphere. show that the electric field inside this atom is : ein=ze4πϵ0(1r^2−rr^3). b. what is the electric field at the surface of the atom? is this the expected value? explain. c. a uranium atom has z = 92 and r = 0.10 nm. what is the electric field at r = r/2?