First slide

Photo Electric Effect

Question

A surface is irradiated with ultra violet radiation of wavelength 0.2 $μ$ m. if the maximum velocity of electron liberated from the surface is 8.8 x 10⁵m/s then the work function of the surface is

Moderate

A

3 eV
B

5 eV
C

5eV
D

6eV

Solution

$E = \frac{hc}{λ} = \frac{(6 \cdot 6 \times 10^{- 34}) \times (3 \times 10^{8})}{0 \cdot 2 \times 10^{- 6}} = 9 \cdot 9 \times 10^{- 19} J Further, E = \frac{1}{2} {mv}^{2} + W_{0} or W_{0} = E - \frac{1}{2} {mv}^{2} W_{0} = 9 \cdot 9 \times 10^{- 19} - \frac{1}{2} \times (9 \cdot 1 \times 10^{- 31}) \times {(8 \cdot 8 \times 10^{5})}^{2} or W_{0} = 9 \cdot 9 \times 10^{- 19} - 3 \cdot 52 \times 10^{- 19} or W_{n} = 6 \cdot 38 eV \approx 6 eV$

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