1.

Radiations of wavelenght 200nm propagating in the form of a parallel beam, fall normally on a plane metallic surface. The intensity of thebeam is 5nW and its cross sectional area 1.0mm^(2). Find the pressure exerted by the radiation on the metallic surface, if the radition is completely reflected.

Answer»

<P>

Solution :`thereforeE=(12400)/(lambda)=(12400)/(2000)=6.2eV~~10^(-18)j`
Number of photons passing a point per second is
`n=(P)/(E)=(5xx10^(-9))/(10^(-18))=5xx10^(9)` momentum of each photon.
`p=(E)/(C)=3.3xx10^(-27)j//s.`
Change in momentun after each STRIKE
`2p = 6.6x 10^(-27) j//s`
Total momentum change per second is
`F=(dp)/(dt)=(nxx2p)/(t)=5xx10^(9)xx6.6xx10^(-27)`
`=33 xx 10^(-18)N`
`therefore` pressure `(F)/(A) = 33 xx 10^(-12) N//m^(2)`


Discussion

No Comment Found

Related InterviewSolutions