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How many photons per second does the laser emit?

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How many photons per second does the laser emit?

Post  pplantblues on Sat Nov 22, 2008 2:39 pm

The power of a red laser (lambda=630 nm) is 3.5 watts (abbreviated W, where 1 W= 1 J/s)=
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Re: How many photons per second does the laser emit?

Post  funion987 on Sat Nov 22, 2008 2:57 pm

I'm, not 100% sure this is right, but this is how I would solve it.

First, figure out the energy that one photon of red (630 nm) light has using Planck's equation.

E= hν

Energy (in joules)= Planck's constant (6.63 x 10-34) x frequency (in meters)

E= 6.63 x 10-34(630 x 10-9 m)

E= 4.18 x 10-40 J
This is the energy in 1 photon of 630 nm light.

Since the problem gives us that the energy is 3.5 W or 3.5 J/s, we need to find out how many photons with the energy above we would need to produce 3.5 J. SO we divide:

3.5/(4.18 x 10-40) = 8.37 x 1039 photons
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Re: How many photons per second does the laser emit?

Post  pplantblues on Sat Nov 22, 2008 3:12 pm

This is what I got for an answer:
E=hc/landa=(6.626x10^-34 J/s)(3.00x10^8 m/s)/6.3x10^-7 m= 3.15x10^-19J
630nm x (10^-9/1 nm)=6.3 x 10^7 m
Since 1 W= 1 J/s
3.50 watts= 3.5 J/s
So 3.5 J/s / 3.15 x 10^-19= 1.11 x 10^-19 photons/s

Thanks for trying.
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Re: How many photons per second does the laser emit?

Post  funion987 on Sat Nov 22, 2008 3:20 pm

You know what, I totally screwed that one up. Maybe it's best if I don't answer if I don'y know. Sorry. Embarassed
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Re: How many photons per second does the laser emit?

Post  pplantblues on Sat Nov 22, 2008 3:29 pm

Don't worry about it ! You still rock
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