The work function of a metal is ` 2,5 xx (10^-19) J`. (a) Find the threshold frequency for photoelectric emission. (b) If the metal is exposed to a light beam of frequency `(6.0 xx 10^14)` Hz, what will be the stopping potential ?

Explanation

Given ` W_0 = 2.5 xx 10^(-19) J `
(a) we have `W_0 = hv_0`
or ` V_0 = W_0 / h `
`= 2.5 xx 10^(-19) / 6.063 xx10^(-34) `
`= 3.77 xx 10^(14) Hz`
`= 3.8 xx 10^(14) Hz`
(b) ` eV_0 = hv - W_0 `
or, V_0 = hv - W_0 / e `
` = 6.63 xx 10^(-34) xx 6 xx 10^(14) - 2.5 xx 10^(-19) / 1.6 xx 10^(-19) `
`= 6.97 xx 10^(-19) - 2.5 xx 10^(-19) / 1.6 xx 10^(19) `
`0.91 V`