First slide

Photo Electric Effect

Question

$10^{- 3}$ walt of 5000 $\overset{o}{A}$ light is directed on a photoelectric cell. If the current in the cell is 0.16 $μ A$ , the percentage of incident photons which produce photo electrons, is

Moderate

A

40%
B

0.04%
C

20%
D

10%

Solution

Energy of each photo $= h c / λ = \frac{12400}{5000} e V = 2.48 e V = 2.48 \times e$ Joule
Number of photons striking the target metal $\frac{p}{2.48 \times e} = \frac{10^{- 3}}{2.48 \times e} S^{- 1}$
Number of electrons affected per second from the metal surface $= \frac{i}{e} = \frac{0.16 \times 10^{- 6}}{e}$
$∴$ Efficiency $= \frac{0.16 \times 10^{- 6} / e}{10^{- 3} / 2.48 \times e} \times 100 % = \frac{0.16 \times 10^{- 6} \times 2.48}{10^{- 3}} \times 100 % = 0.04 %$

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