Question

The work function of the following metals is given: $Na=2.75eV,K=2.3eV,Mo=4.17eV$ and $Ni=5.15eV$. Which of these metals will not undergo photoelectric emission for radiation of wavelength $3300\stackrel{\circ }{A}$ from a laser source placed $1m$ away from these metals? What happens if the laser source is brought closer and placed $50cm$ away?

Answer 1

Energy of the incident photon:

$E=\frac{hc}{\lambda }=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{3300\times {10}^{-10}\times 1.6\times {10}^{-19}}=3.75eV$

$M_{\circ }$ and $N_i$ will not undergo photoelectric emission as the work function for these materials is higher than the energy of the incident photon. Also, bringing the source closer only changes the intensity and not the energy of the incident photon, therefore these materials will not undergo photoelectric emission.