First slide

Photo Electric Effect

Question

Electron from n = 2 to n =1 in Hydrogen atom is made to fall on a metal surface with work function 1.2 eV. The maximum velocity of photo electrons emitted is nearly equal to

Moderate

A

$6 x 10^{5} m / s$
B

$3 x 10^{5} m / s$
C

$2 x 10^{5} m / s$
D

$8 \sqrt{5} x 10^{5} m / s$

Solution

$E n e r g y o f t h e p h o t o n i s e q u a l t o 13.6 - 3.4 = 10.2 e V k i n e t i c e n e r g y o f t h e p h o t o n i s 10.2 - 1.2 = 9 e V \frac{1}{2} m v^{2} = 9 x 10^{- 19} t a k i n g m = 9 x 10^{- 31} k g v = 8 \sqrt{5} x 10^{5}$

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