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Home Q & A Board Science-Related Homework Help Physics
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tmd0068 tmd0068
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11 years ago
How many photons are emitted every 0.260 s by a 139.0 W sodium lamp if the wavelength of sodium light is 1240 nm? Planck?s constant is 6.63 × 10?34 J ? s and the speed of light is 3 × 108 m/s. Answer in units of photons.
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wrote...
#1
11 years ago
I'll try to outline the problem for you so you can lead yourself to the answer.

A Watt is a Joule/Second, so by telling you a time interval and wattage, they are specifying the amount of joules, which is an amount of energy, where E = 139W*.26S = ___ Joules

We'll assume for simplicity that all photons have the wavelength 1240nm (on average this is true so its fine). We can figure the amount of energy per photon by E = hc/lambda = joules/photon. Actually this may come out in electron volts depending on your choices for the constants, but you can convert easily enough.

Now you know the energy per photon and the total amount of energy being produced, solve for the # of photons required to produce said energy.
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ripsmithyripsmithy
wrote...
#2
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11 years ago
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