InterviewSolution
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InterviewSolution
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Light with an energy flux of `40W//cm^(2)` falls on a non-reflecting surface at normal incidence. If the surface has an area of `20cm^(2)`, find the average force exerted on the surface during a `30min` time span. |
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Answer» The energy incident on surface is `U = Iat = 40 xx 10^(4) xx 20 xx 10^(-4) xx 30 xx 60` `= 1.44 xx 10^(6)J` Total momentum delivered (for completa absorption) `p = (U)/(c ) = (1.44 xx 10^(6))/(3xx10^(8)) = 0.48 xx 10^(-2)kgm//sec` The average force extered on surface `F = (p)/(t) = (0.48xx10^(-2))/(30xx60) = 0.27 xx 10^(-5)N` |
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