Question

What is the maximum wavelength of light that will cause photo electrons to be emitted

from sodium? What will the maximum kinetic energy of the photo electrons be if 200-nm

light falls on a sodium surface?

Answer 1

Gives

$\lambda=200nm$

$\lambda=\frac{hc}{\phi}$

$\lambda=\frac{6.625\times10^{-34}\times3\times10^{8}}{2.3\times1.6\times10^{-19}}$

$\lambda=\frac{1.9875\times10^{-25}}{3.68\times10^{-19}}=5.40\times10^{-7}m$

$\lambda=540nm$

Maximum kinetic energy

$E=\frac{hc}{\lambda}-\phi$

$$E=\frac{6.625\times10^{-34}\times3\times10^8}{200\times10^{-9}}-2.3=6.2041-2.3$$

$E=3.9041eV$

$E=3.9eV$