Question

Plot a graph showing the variation of photoelectric current with intensity of light. The work function for the following metals is given:
Na: 2.75 eV and Mo : 4.175 eV.
Which of these will not give photoelectron emission from a radiation of wavelength 3300

\[A^\circ\] from a laser beam? What happens if the source of laser beam is brought closer?

Answer 1

The plot between photoelectric current and intensity of light varies linearly as shown below:

Given that λ = 3300

\[\times {10}^{- 10}\] m,

\[\phi_{Na} = 2 . 75 eV, \phi_{Mo} = 4 . 175 eV\]

Then energy of the laser beam is

\[E = \frac{hc}{\lambda} = \frac{6 . 6 \times {10}^{- 34} \times 3 \times {10}^8}{3300 \times {10}^{- 10} \times 1 . 6 \times {10}^{- 19}} = 3 . 75 eV\]

Since 

\[E < \phi_{Mo}\] therefore there will be no emission of photoelectrons for Molybdenum (Mo).
Bringing the source nearer will bring no change as photoelectric effect is independent of the distance of the source.