Surface of certain metal is first illuminated with light of wavelength ${\lambda }_1$ =350 nm and then, by light of wavelength ${\lambda }_2$= 540 nm. It is found that the maximum speed of the photo electrons in the two cases differ by a factor of 2. The work function of the metal (in eV) is close to:(Energy of photon =$\frac{1240}{\lambda \left(innm\right)}eV$ )