A laser used in eye surgery emits a 3.00mJ pulse in 1.00 ns, focused to a spot 2

Question

A laser used in eye surgery emits a 3.00mJ pulse in 1.00 ns, focused to a spot 20.0 µm in diameter on the retina. (a) Find (in SI units) the power per unit areaat the retina. (This quantity is called theirradiance.)
W/m2

(b) What energy is delivered per pulse to an area of molecular size(say, a circular area 0.700 nm indiameter)?
J (a) Find (in SI units) the power per unit areaat the retina. (This quantity is called theirradiance.)
W/m2

(b) What energy is delivered per pulse to an area of molecular size(say, a circular area 0.700 nm indiameter)?
J

Explanation / Answer

a) Power is            P = E/t                =(3.00*10-3J)/(1.00*10-9s) The power per unit area at the retina is             P/A = P /(4r2) Here r = 10.0*10-6m b) The energy delivered per pulse to an area ofmolecule size is             P' = (P/A)(4R2) Here R = 0.35 *10-9m substitute the values.

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