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Help in aprobelem

Posted: Thu Jul 29, 2010 5:22 am
by ahmedfawzika
i have a problem and i need a solution to it,
What is the smallest spot you can focus from a sun ideal parallel beam of light with a lens of D= 10 cm and F focal length= 100 cm knowing that power density of the sun is 1 KW/ M2?

and if the focused spot is 1mm in diameter, what is the sun power density in the spot?

i hope that some one can help me....
thanks a lot