First slide

Photo Electric Effect

Question

Mercury violet tight $(λ = 4558 \overset{o}{A})$ is falling on a photosensitive material (Φ = 2.5 eV). The speed of the ejected electrons is in ms^-l. about

Moderate

A

$3 \times 10^{5}$
B

$2.65 \times 10^{5}$
C

$4 \times 10^{4}$
D

$3.65 \times 10^{7}$

Solution

$\begin{array}{l} By using E = W_{o} + \frac{1}{2} {mv}_{\max}^{2}; where \\ E = \frac{12375}{4558} = 2 .71 eV \\ \Rightarrow 2 .71 eV = 2 .5 eV + \frac{1}{2} \times 9 .1 \times 10^{- 31} \times v_{\max}^{2} \\ \Rightarrow 0 .21 \times 1 .6 \times 10^{- 19} = \frac{1}{2} \times 9 .1 \times 10^{- 31} \times v_{\max}^{2} \\ \Rightarrow v_{\max} = 2 .65 \times 10^{5} m / s \end{array}$

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