Work function of a metal is 4.0 eV. Find the maximum value of wavelength of a radiation that can emit photoelectrons from the metal.

Explanation

Let, threshold frequency = `f_(0)`, threshold wavelength = `lamda_(0)` and work function `= W_(0)`
`:. W_(0) = hf_(0) = (hc)/(lamda_(0)) or, lamda_(0) = (hc)/(W_(0))`
Give, `W_(0) = 4.0 eV = 4 xx 1.6 xx 10^(-12)` erg,
we know, `h = 6.60 xx 10^(-27)` erg.s
and `c = 3 xx 10^(10) cm.s^(-1)`
`:. lamda_(0) = (6.60 xx 10^(-27) xx 3 xx 10^(10))/(1.6 xx 10^(-12) xx 4) cm`
`= 3.09375 xx 10^(-5) cm ~~ 3094 Å`