Answer:
2.13 x 10^-19 J or 0.53 eV
Explanation:
cut off wavelength, λo = 700 nm = 700 x 10^-9 m
λ = 400 nm = 400 x 10^-9 m
Use the energy equation
[tex]E = \frac{h c}{\lambda _{o}}+K[/tex]
Where, K be the work function
[tex]\frac{h c}{\lambda} = \frac{h c}{\lambda _{o}}+K[/tex]
[tex]K =hc\left ( \frac{1}{\lambda } -\frac{1}{\lambda _{0}}\right )[/tex]
[tex]K =6.63\times 10^{-34}\times 3\times 10^{8}\left ( \frac{1}{4\times 10^{-7} } -\frac{1}{7\times 10^{-7}}\right )[/tex]
K = 2.13 x 10^-19 J
K = 0.53 eV
