Q.16.  The following table gives the values of work function for a few photo sensitive metals.
 

S.NO	METAL	WORK FUNCTION (eV)
1	Na	1.92
2	K	2.15
3	Mo	4.17

In each of these metals is exposed to radiations of wavelength 300mm, which of them will not emit photo electrons and why?

OR

By how much would the stopping potential for a given photosensitive surface go up if the frequency of the incident radiations were to be increased from $$\begin{gathered} 4\times {10}^{15} Hz to 8\times {10}^{15 }Hz? \\ Given h= 6.4\times {10}^{-34} J -s,e=1.6\times {10}^{-19} C and c=3\times {10}^8 m{s}^{-1} \end{gathered}$$