First slide

Photo Electric Effect

Question

Light of wavelength 4000 $\overset{o}{A}$ is incident on a metal plate whose work function is 2 eV. What is maximum kinetic energy of emitted photoelectron?

Moderate

A

2.0 eV
B

1.1 eV
C

0.5 eV
D

1.5 eV

Solution

If the maximum kinetic energy of photoelectrons emitted from metal surface is E_o and W is the work function of metal then
$E_{k} = hv - W$
where Iv is the energy of photon absorbed by the electron in metal.
$\begin{array}{l} ∴ E_{k} = \frac{hc}{λ} - W \\ wherev = \frac{c}{λ} \\ Putting the numerical values, we have \\ E_{k} = [\frac{6 .6 \times 10^{- 34} \times 3 \times 10^{8}}{4000 \times 10^{- 10} \times 1 .6 \times 10^{- 19}} - 2] eV \\ E_{k} = 3 .1 - 2 = 1 .1 eV \end{array}$

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