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 : (Energjr of photon = ${1240\over\lambda(\text{in nm})}$eV )
(1) 1.8
(2) 1.4
(3) 2.5
(4) 5.6
(1) 1.8
(2) 1.4
(3) 2.5
(4) 5.6