# physics

Light is shining perpendicularly on the surface of the earth with an intensity of 680 W/m2. Assuming that all the photons in the light have the same wavelength (in vacuum) of 478 nm, determine the number of photons per second per square meter that reach the earth.

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1. Energy =Power x time =680 W/m2 x 1 second =680 Joule/m2
Energy of 1 photone = hf =hc/λ
Number of photones =Energy/energy of 1 photon =
N=680• λ/hc=680•478•10⁻⁹/6.63•10⁻³⁴•3•10⁸=…

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2. Thank You So much

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