Threshold frequency for a metal is ${10}^{15}$ Hz. Light of $\mathrm{\lambda }$ = 4000 $\stackrel{\mathrm{o}}{\mathrm{A}}$ falls on its surface. Which of the following statements is correct?

$\begin{array}{l}\mathrm{Frequency}\mathrm{of}\mathrm{light}\mathrm{of}\mathrm{wavelength}\left(\mathrm{\lambda }=4000\stackrel{\mathrm{o}}{\mathrm{A}}\right)\mathrm{is}\\ \mathrm{v}=\frac{\mathrm{c}}{\mathrm{\lambda }}=\frac{3\times {10}^8}{4000\times {10}^{-10}}=0.75\times {10}^{15}\end{array}$

which is less than the given threshold frequency. Hence no photoelectric emission takes place.