The stopping potential for photoelectrons emitted from a surface illuminated by light of wavelength 6630 is 0.42 V. If the threshold frequency is x ×…

The stopping potential for photoelectrons emitted from a surface illuminated by light of wavelength $\displaystyle 6630 \AA$ is $\displaystyle 0.42$ V . If the threshold frequency is $\displaystyle x \times 10^{13} / \mathrm{s}$, where $\displaystyle x$ is \_\_\_\_ (nearest integer). (Given, speed light $\displaystyle =3 \times 10^8 \mathrm{~m} / \mathrm{s}$,Planck's constant $\displaystyle =6.63 \times 10^{-34} \mathrm{Js}$ )