The difference between threshold wavelengths for two metal surfaces A and B having work function φ_A=9 e V and φ_B=4.5 e V in nm is: {Given, hc =1242…

The difference between threshold wavelengths for two metal surfaces $\displaystyle A$ and $\displaystyle B$ having work function $\displaystyle \phi_A=9 e V$ and $\displaystyle \phi_B=4.5 e V$ in nm is: {Given, $\displaystyle \mathrm{hc}=1242 \mathrm{eV} \mathrm{nm}$ }