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
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