Shining the light, PHYSICS help
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Shining the light, PHYSICS help

[From: ] [author: ] [Date: 12-05-11] [Hit: ]
681/2.42*10^-19 = 2.......
Light is shining perpendicularly on the surface of the earth with an intensity of 681 W/m2. Assuming all the photons in the light have the same wavelength (in vacuum) of 823 nm, determine the number of photons per second per square meter that reach the earth.

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just find the energy in one photon

823 nm = 823*10^-9

E = h*f

f = c/L

where L is wavelength

E = h* c/L

E = 6.626*10^-34*3*10^8 / 823*10^-9

E = 2.42 *10^-19 Joules per photon

P = E/s

681 J/sm^2 = intensity

681/2.42*10^-19 = 2.81 * 10^+21 photons /s m^2

thats the answer
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