Find the potential difference av, required to stop an electron (called a 'stopping potential) moving with an initial speed of 1.89 x 10' m/s. (b) would a proton traveling at the same speed require a greater or less magnitude potential difference? explain this answer has not been graded yet (c) find a symbolic expression for the ratio of the proton stopping potential and the electron stopping potential, av, jav, the answer should be in terms of the proton mass m, and electron mass me