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![[Post New]](/templates/default/images/icon_minipost_new.gif) 12 Nov 2007 23:08:54 IST
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A beam of white light is incident normally on a plane surface absorbing 70 % of the light and reflecting the rest. if the incident beam carries 10 W of power, find the force exerted by it on the surface.
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13 Nov 2007 14:13:02 IST
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10W means 10 joule energy incident in 1 sec.
So, 70% absorption means 7J energy in 1 sec.
Now, momentum transfered=dP = Energy transfered / c
where c = speed of light.
dP = 7 / c
Force = dP/dT
Here dT =1 sec as dP is calculated for 1 sec only.
Force = 7/c = 2.33 x 10 - 8 N
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13 Nov 2007 20:20:00 IST
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Perfect explaination Rooney
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The most incomprehensible thing about the world is that it is
at all comprehensible. |
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19 Nov 2007 14:43:21 IST
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well rooney is wrong
here 30% of the light is reflected .so we have to consider that too.
the momentum of 30% light is changed by twice the amount
consider that also and u will get the correct ans
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but sooner or later the man who wins
is the man who thinks "HE CAN" |
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