Determining the number of photons that reach the earth

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AI Thread Summary
Light with an intensity of 910 W/m² and a wavelength of 668 nm results in approximately 3.066 x 10²¹ photons per second per square meter reaching Earth. The calculation uses the formula for photon flux, incorporating Planck's constant and the speed of light. A minor correction was noted regarding the speed of light notation, which can be expressed in scientific notation for computer entries. The discussion highlighted the importance of significant figures based on the given values. Overall, the calculations and concepts were confirmed to be correct, with tips provided for entering answers in a specific format.
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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
 
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Looks good!

Just a small typo, c is 3x10^[/size]+8. Looks like you used the correct value for the calculation though.[/size]
 
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 doesn't let us put x10^21), so I was assuming I must've done something wrong.. :-/
 
Looks like 3 significant figures are justified here, given the values of intensity and wavelength.

By the way, if you are entering numbers into a computer, you can usually write them as
6.63e-34
3e8​
The "e" is pretty standard notation for computer entry, and simply means "times 10 to the ___ power"

For example:
http://www.google.com/search?hl=en&q=910*668e-9/(6.63e-34*3e8)&btnG=Search
 
Oh wow, I never knew I could write my answers that way on this program. haha thanks!
 
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