A) \[\frac{nch}{\lambda }\]
B) \[\frac{{{n}^{2}}h}{2\lambda }\]
C) \[\frac{2nh}{c\,\lambda }\]
D) \[\frac{n{{h}^{2}}}{{{\lambda }^{2}}}\]
E) \[\frac{nh}{\lambda }\]
Correct Answer: E
Solution :
As energy of photon \[E=\frac{hc}{\lambda }\] Number of photons falling per second on the surface is \[n=\frac{W}{E}=\frac{W}{\frac{hc}{\lambda }}=\frac{W\lambda }{hc}\] The total momentum of photons falling per second on the surface is \[\Delta P=\frac{W}{c}=\frac{nhc}{\lambda c}=\frac{nh}{\lambda }\] The rate of change of momentum of the surface i.e. force on the surface \[F=\frac{\Delta P}{\Delta t}=\frac{nh}{\frac{\lambda }{1\,s}}=\frac{nh}{\lambda }\]
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