The beam of light has three wavelengths 4144AA, 4972AA, 6216AA with a total intensity of 3.6×10⁻3W/m² equally distributed among the three wavelengths. The beam falls normally on a clean metallic surface of work function 2.3eV. Assuming no loss by reflection and that each photon ejects one photoelectron, calculate the number of photoelectrons liberated in 2s.
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Always check threshold wavelength before counting photoelectrons.