First slide

Photo Electric Effect

Question

A photosensitive metallic surface has work function, ${hv}_{o}$ . If photons of energy 2 ${hv}_{o}$ fall on this surface, the electrons come out with a maximum velocity of 4 x $10^{6}$ m./s. When the photon energy is increased to 5 ${hv}_{o}$ , then maximum velocity of photoelectrons will be

Moderate

A

2 x $10^{6}$ m./s
B

2 x $10^{7}$ m./s
C

8 x $10^{5}$ m./s
D

8 x $10^{6}$ m./s

Solution

Einstein's photoelectric equation can be written as
$\begin{array}{l} \frac{1}{2} {mv}^{2} = hv - ϕ \Rightarrow \frac{1}{2} m \times {(4 \times 10^{6})}^{2} = 2 {hv}_{o} - {hv}_{o} . . (i) \\ and \frac{1}{2} m \times v^{2} = 5 {hv}_{o} - {hv}_{o} . . . . . (ii) \\ Diving Eq . (ii) by (i), we get \frac{v^{2}}{{(4 \times 10^{6})}^{2}} = \frac{4 {hv}_{o}}{{hv}_{o}} \\ \Rightarrow v^{2} = 4 \times 16 \times 10^{12} \Rightarrow v^{2} = 64 \times 10^{12} \Rightarrow v = 8 \times 10^{6} m / s \end{array}$

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