Light with an energy flux of 18 W//cm^(2) falls on a non reflecting 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.

Light with an energy flux of 18 W//cm^(2) falls on a non reflecting su

1.	Light with an energy flux of 18 W//cm^(2) falls on a non reflecting 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» Solution :The TOTAL energy falling on the SURFACE is `U=(18 W//cm^(2))xx(20 cm^(2))xx(30xx60)` `=6.48 xx 10^(5) J` Therefore, the total momentum delivered (for complete absorption) is `P=(U)/(C)=(6.48xx10^(5) J)/(3xx10^(8) m//s) =2.16xx10^(-3) kg m//s` The average force exerted on the surface is `F=(P)/(t)=(2.16xx10^(-3))/(0.18xx10^(4))=1.2xx10^(-6) N`

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Light with an energy flux of 18 W//cm^(2) falls on a non reflecting 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.

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