(a) Find the electric potential difference ?Ve required to stop an electron (cal

Question

(a) Find the electric potential difference ?Ve required to stop an electron (called a "stopping potential") moving with an initial speed of 2.13 107 m/s.
(b) Would a proton traveling at the same speed require a greater or lesser magnitude of electric potential difference?
a. greater
b. lesser
c. equal
Explain why this is so.
(c) Find a symbolic expression for the ratio of the proton stopping potential and the electron stopping potential, ?Vp/?Ve. (Use the following as necessary: mp for the mass of proton and me for the mass of electron.)

Explanation / Answer

a) According to work energy theorem         Work done = Change in kinetic energy             eV = (1/2)mv^2 - (1/2)mu^2 Here e =1.6 x 10^-19 C          m =9.11 x 10^-31 kg         u = 0         v = 2.13107 m/s So the electric potential difference is             V = [ (1/2)mv^2 - (1/2)mu^2]/(e)                 = [mv^2]/(2e)                 = [(9.11x10^-31kg)( 2.13107 m/s)^2]/(2(1.6 x 10^-19C))                 = 1.293x10^-11 V b) greater that is option (a) is correct. because electric potential is directly proportional to mass. Since mass proton is greater than mass of electron. c) The ratio of the proton stoping potential and the electron stopping potential is                Vp/Ve = mp/me b) greater that is option (a) is correct. because electric potential is directly proportional to mass. Since mass proton is greater than mass of electron. c) The ratio of the proton stoping potential and the electron stopping potential is                Vp/Ve = mp/me

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