InterviewSolution
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InterviewSolution
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Light with an energy flux` 20 W//cm^2` falls on a non-reflecting surface at normal incidence. If the surface has an area of `30 cm^2`. the total momentum delivered ( for complete absorption)during 30 minutes isA. `36 xx 10^(-5) kg-m//s`B. `36 xx 10^(-4) kg-m//s`C. `108 xx 10^(4) kg-m//s`D. `1.08 xx 10^(7) kg-m//s` |
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Answer» Correct Answer - B Given energy flux `phi =20W//cm^(2)` Area `A = 30cm^(2)` Time , `t= 30min =30 xx 60s` Now , total energy falling on the surface in time is `u=phiAt =20 xx 30 xx (30 xx 60)J` Momentum of the incident light `=U/C` `=(20 xx 30 xx (30 xx 60))/(3xx 10^(8)) rArr = 36 xx 10^(-4) kg-ms^(-1)` Momentun of the reflected light =0 `:.` Momentum delivered to the suface `=36 xx 10^(-4) -0 =36 xx 10^(-4) kg-ms^(-1)` |
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