When light of sufficiently short wavelength falls on the ball, photoelectrons are ejected and the copper ball gains positive change. The changes ball tends to resist further emission of electorns by attracting them. When the copper ball has enough change even the most energetic electrons are unable to leave it. We can calculate this final maximum potential of the copper ball. It is obviously equal in magnitude (in volt) to the maximum `K.E.` of electrons (in electron volts) initially emitted. Hence
`varphi_(max) = (2picancelha c)/(lambdae) - A_(cu)`
`= 8.86 - 4.47 = 4.39` volts
`(A_(cu)` is the work function of copper.)
