In a photoelectric experiment, the relation between the applied potential difference $\mathrm{V}$ and the photoelectric current $\mathrm{I}$ was found to be as shown in the graph below. If the work function of the cathode plate is $28.8\text{ eV}$ and $\mathrm{h}=6.6\times {10}^{-34 }\mathrm{J} \mathrm{s}$, the frequency of incident radiation would be nearly $\left(\mathrm{in}\mathrm{ }{\mathrm{s}}^{-1}\right)$