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Light with an energy flux of 18 W//cm^(2) falls on a nonreflecting surface at normal incidence. If the surface has an area of 20 cm^(2), find the average force exerted on the surface during a 30 minute time span. |
Answer» <html><body><p></p>Solution :The <a href="https://interviewquestions.tuteehub.com/tag/total-711110" style="font-weight:bold;" target="_blank" title="Click to know more about TOTAL">TOTAL</a> energy falling on the surface is <br/> `<a href="https://interviewquestions.tuteehub.com/tag/u-1435036" style="font-weight:bold;" target="_blank" title="Click to know more about U">U</a>=(18 W//cm^(<a href="https://interviewquestions.tuteehub.com/tag/2-283658" style="font-weight:bold;" target="_blank" title="Click to know more about 2">2</a>))xx(20 cm^(2))xx(30xx60 s)` <br/> `=6.48 xx10^(5) J` <br/> Therefore, the total momentum <a href="https://interviewquestions.tuteehub.com/tag/delivered-7259798" style="font-weight:bold;" target="_blank" title="Click to know more about DELIVERED">DELIVERED</a> (for complete absorption) is <br/> `p=(U)/(c )=(6.48xx10^(5) J)/(3xx10^(8) m//s)=2.16 xx10^(-3) kg m//s` <br/> The <a href="https://interviewquestions.tuteehub.com/tag/average-13416" style="font-weight:bold;" target="_blank" title="Click to know more about AVERAGE">AVERAGE</a> force exerted on the surface is <br/> `F=(p)/(t) =(2.16 xx10^(-3)/(0.18xx10^(4))=1.2xx10^(-6) N` <br/> How will your result be modified if the surface is a perfect reflector?</body></html> | |