The work function for tungsten and sodium are 4.5 eV and 2.3 eV, respectively. If the threshold wavelength λ for sodium is 5600 Å, then the value of λ for tungsten is:

2862 Å

Work function, $\phi_0=\frac{hc}{λ_0}$

$∴\frac{(\phi_0)_T}{(\phi_0)_{Na}}=\frac{λ_{Na}}{λ_T}$ or $λ_T\frac{λ_{Na}×(\phi_0)_{Na}}{(\phi_0)_T}=\frac{5600×2.3}{4.5}=2862Å$