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 = 20 W//cm^(2)` Area, `A = 30 cm^(2)` Time, `t = 30` min = `30 xx 60 s` Now, total energy following on the surface in time t is, `u = phi At = 20 xx 30 xx (30 xx 60) J` Momentum of the incident light `= U/c` `= (20 xx 30 xx (30 xx 60))/(3 xx 10^(8)) = 36 xx 10^(-4) kg-m//s` Momentum of the reflected light `= 0` `:.` Momentum delivered to the surface `= 36 xx 10^(-4) -0 = 36 xx 10^(-4) kg-m//s` |
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