Determining the number of photons that reach the earth

  • Thread starter phys62
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  • #1
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Homework Statement


Light is shining perpendicularly on the surface of the earth with an intensity of 910 W/m2. Assuming all the photons in the light have the same wavelength (in vacuum) of 668 nm, determine the number of photons per second per square meter that reach the earth.



Homework Equations


The power per area is:
P/A = (# of photons /t /A)*(energy / photon)

E/photon = h nu = hc / lambda

photons /t /A = (P/A) * lambda / hc


The Attempt at a Solution


photons /t /A = (P/A) * lambda / hc
photoms /t /A = (910)*(668x10^-9)/(6.63x10^-34)(3x10^-8) = 3.066x10^21
 

Answers and Replies

  • #2
Redbelly98
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Looks good!

Just a small typo, c is 3x10^+8. Looks like you used the correct value for the calculation though.
 
  • #3
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The program I enter my homework answers into doesn't let me have that many decimal places in my answer though (we have to write it out long, it doesnt let us put x10^21), so I was assuming I must've done something wrong.. :-/
 
  • #5
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Oh wow, I never knew I could write my answers that way on this program. haha thanks!
 

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