Problem

A beam of light has three wavelengths

4144 \text{ \AA}

4972 \text{ \AA}

and

6216 \text{ \AA}

with a total intensity of

3.6 \times 10^{-3} \text{ Wm}^{-2}

equally distributed amongst the three wavelengths. The beam falls normally on an area

1.0 \text{ cm}^2

of a clean metallic surface of work-function

2.3 \text{ eV}

. Assume that there is no loss of light by reflection and that each energetically capable photon ejects one electron. Calculate the number of photoelectrons liberated in two seconds.

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