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03-23-2011, 11:44 PM #1
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SportyPhysicist
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Power calculations

Hi guys

I'm new to this, but i've seen alot of post relating to the power of lasers and think a good way to visualize it is heating power ie temperature increase of water in 1 second.

I know C=Q/ΔT where C =Specific heat, Q =heat and T =temperature
and dimensionless heat capacity = C / Nk where n is number of molecules and k is the Boltzmann's constant
energy of photon = hc/λ where h is planks constant, c is speed of light and λ is wavelength

What i don't understand is how the labeled power corresponds to the energy of the photons or how to use this to calculate Q heat transfer.

Thnaks for you help

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03-24-2011, 12:20 AM #2
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anselm
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Re: Power calculations

I don't know if this helps any, but go to this page and scroll down a little until you
reach the part where she uses a mug filled with water to measure the power
of her CO2 laser
Diane's Laser Page

In any case, I think you need an object immersed in the water that can absorb the
lase radiation and pass off the heat to the water, since the water itself has
a hard time absorbing the laser radiation directly.
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03-24-2011, 12:25 AM #3
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Cyparagon
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Re: Power calculations

It might be right in its own way, but that's kind of a strange way to put it. I was always taught:

Q=CmΔT

All the same variables with the addition of mass m.
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03-24-2011, 10:10 AM #4
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SportyPhysicist
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Re: Power calculations

in response to Cyparagon: I agree Q=CmΔT is a better/easier equation to use.

In response to anselm: I was thinking more about how much energy is carried in the laser beam. Then i can build on this to calculate absorption in different materials, conductance and energy densities ( affect of lenses).

Cheers

03-27-2011, 02:19 PM #5
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BennyF
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Re: Power calculations

well you could use the equation E = n*e where n= the number of photons and e= the energy of the photon. Also you can use E = nhf where h= Planck's constant and f= frequency. P= E/t, P=nhf/t t= time for a time of 1s t is removed from the equation. P=nhf=nhc/l c= the speed of light and l= the wavelength.
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Last edited by BennyF; 03-30-2011 at 12:09 PM.

 Tags calculations, energy, maths, power, specific heat

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