Answer
given,
work function of gold = 4.90 eV
work function of cesium = 1.90 eV
using energy equation
[tex]E = \dfrac{hc}{\lambda}[/tex]
h is plank's constant
c is the speed of light
[tex]\lambda = \dfrac{hc}{E}[/tex]
for gold
[tex]\lambda_g = \dfrac{6.624\times 10^{-34}\times 3\times 10^8}{4.90\times 1.6\times 10^{-19}}[/tex]
[tex]\lambda_g = 2.535\times 10^{-7}\ m[/tex]
[tex]\lambda_g = 0.254\ \mu m[/tex]
for cesium
[tex]\lambda_c = \dfrac{6.624\times 10^{-34}\times 3\times 10^8}{1.90\times 1.6\times 10^{-19}}[/tex]
[tex]\lambda_c = 6.537\times 10^{-7}\ m[/tex]
[tex]\lambda_c = 0.654\ \mu m[/tex]
