Question

The work function of sodium metal is 2.3 eV. What is the longest wavelength of light that cause

photoelectric emission from sodium

Answer 1

Work function W = 2.3 eV

$1\; eV = 1.6 \times 10^{-19} \;J \\ W = 2.3 \times 1.6 \times 10^{-19} = 3.68 \times 10^{-19} \;J$

longest wavelength $λ_0$ will be

$W= \frac{hc}{λ_0} \\ λ_0 = \frac{hc}{W} \\ h=6.626 \times 10^{-34} \;Js \\ c= 3 \times 10^8 \;m/s \\ λ_0 = \frac{6.626 \times 10^{-34} \times 3 \times 10^8}{3.68 \times 10^{-19}} \\ = 5.4 \times 10^{-7} \;m$