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Surface of certain metal is first illuminated with light of wavelength λ 1 = 350 nm and then, by light of wavelength λ 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 = 1240 (in nm) λ eV)

1. 5.6
2. 2.5
3. 1.8
4. 1.4

Correct answer: 1.8

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