First slide

Photo Electric Effect

Question

The surface of some material is irradiated in turn, by waves of wavelength $λ_{1} = 6.4 \times 10^{- 7} m a n d λ_{2} = 9.8 \times 10^{- 7} m$ respectively. The ratio of stopping potential in two cases is 2 : 1. The work function is _____

Moderate

A

0.42 eV
B

0.32 eV
C

0.59 eV
D

0.23 eV

Solution

$\begin{array}{l} \frac{e {(v_{0})}_{1}}{e {(v_{0})}_{2}} = \frac{\frac{h c}{λ_{1}} - ϕ}{\frac{h c}{λ_{2}} - ϕ} \Rightarrow \frac{2}{1} = \frac{\frac{12400}{6400} - ϕ}{\frac{12400}{9800} - ϕ} \\ \Rightarrow \frac{1.937 - ϕ}{1.265 - ϕ} = 2 \Rightarrow ϕ = 0.593 e V . \end{array}$

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