Dual Nature Of Light Question 356
Question: When a surface is irradiated with light of wavelength $ 4950\overset{o}{\mathop{A}}, $ , a photocurrent appears which vanishes if a retarding potential greater than 0.6 V is applied across the photo tube. When a different source of light is used, it is found that the critical retarding potential is changed to 1.1 V. Find the wavelength of second source.
Options:
A) $ 4077\overset{o}{\mathop{A}}, $
B) $ 992\overset{o}{\mathop{A}}, $
C) $ 628\overset{o}{\mathop{A}}, $
D) $ 238\overset{o}{\mathop{A}}, $
Show Answer
Answer:
Correct Answer: A
Solution:
[a] By Einstein equation $ hf=W_{0}+eV_{0}. $ $ W_{0}=\frac{hc}{\lambda }-eV_{0} $ $ =\frac{( 6.63\times {{10}^{-34}} )\times ( 3\times 10^{8} )}{4950\times {{10}^{-10}}}-( 1.6\times {{10}^{-19}} )\times 0.6 $ $ =3.12\times {{10}^{-19}}J $ For the second surface $ hf’=W_{0}+eV_{0} $ $ \text{or }\frac{hc}{\lambda ‘}=3.2\times {{10}^{-19}}+1.6\times {{10}^{-19}}\times 1.1 $
$ \therefore \lambda ‘=4077\overset{o}{\mathop{A}}, $
BETA
