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Radiations of wavelength 200 nm propagating in the form of a parallel beam, fall normally on a plane metallic surface. The intensity of the beam is 5mW and its cross sectional area 1.0mm^(2). Find the pressure exerted by the radiation on the metallic surface, if the radiation is completely reflected. |
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Answer» SOLUTION :`E=(12400)/(lamda)=(12400)/(2000)=6.2eV~~10^(-18)J` Number of photons passing a POINT per second is `n=(P)/(E)=(5xx10^(-3))/(10^(-18))=5xx10^(15)` MOMENTUM of each photon `p=(E)/(C)=3.3xx10^(-27)J//s` Change in momentum after each strike `=2p=6.6xx10^(-27)J//s` TOTAL momentum change per second is `F=(dp)/(dt)=(nxx2p)/(t)=5xx10^(15)xx6.6xx10^(-27)` `=33xx10^(-12)N` `:.` pressure `=(F)/(A)=33xx10^(-6)N//m^(2)` |
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