First slide

Photoelectric effect and study of photoelectric effect

Question

Ultraviolet light of wavelength 300 nm and intensity 1.0 watt/m² falls on the surface of a photosensitive material. lf 1% of the incident photons produce photoelectrons,
then the number of photoelectrons emitted from an area of 1.0 cm² of the surface is nearly

Moderate

A

$9.61 \times 10^{14} per sec$
B

$4.12 \times 10^{13} per sec$
C

$1.51 \times 10^{12} per sec$
D

$2.13 \times 10^{11} per sec$

Solution

Intensity of light,
$\begin{array}{l} I = \frac{Power}{Area} = \frac{n h c}{A λ} \\ \Rightarrow Number of photon per sec, n = \frac{I A λ}{h c} \\ ∴ Number of photo electron per sec = \frac{1}{100} \times \frac{I A λ}{h c} \\ = \frac{1}{100} \times \frac{1 \times 10^{- 4} \times 300 \times 10^{- 9}}{6.6 \times 10^{- 34} \times 3 \times 10^{8}} = 1.51 \times 10^{12} \end{array}$

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