First slide

Photo Electric Effect

Question

Energy required to remove an electron from aluminium surface is 4.2 eV. If light of wavelength 2000 $\overset{o}{A}$ falls on the surface, the velocity of the fastest electron ejected from the surface will be

Moderate

A

$8 .4 \times 10^{5} m / \sec$
B

$7 .4 \times 10^{5} m / \sec$
C

$6 .4 \times 10^{5} m / \sec$
D

$8 .4 \times 10^{6} m / \sec$

Solution

$\begin{array}{l} By using E = W_{o} + \frac{1}{2} {mv}_{\max}^{2} where \\ E = \frac{12375}{2000} = 6 .18 eV \\ \Rightarrow 6 .18 eV = 4 .2 eV + \frac{1}{2} {mv}_{\max}^{2} \Rightarrow 1 .98 eV = \frac{1}{2} {mv}_{\max}^{2} \\ \Rightarrow 1 .98 \times 1 .6 \times 10^{- 19} = \frac{1}{2} \times 9 .1 \times 10^{- 31} \times v_{\max}^{2} \\ \Rightarrow v_{\max} = 8 .4 \times 10^{5} m / s \end{array}$

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App