Designing an experiment to demonstrate Planck's Law

[Andrew774]

For my undergraduate physics lab, we are asked to spend 3 weeks (3 3-hour sessions + any time during the week if I need extra time) doing an experiment of our own choosing. The physics department will provide any experimental tools needed within reason.

I have been considering using this time to measure the intensity vs. wavelength of the light emitted from a tungsten filament at different temperatures. I would do this by focusing the emitted light through a lens then separating the wavelengths with a prism and finally detecting the intensity by wavelength with a spectrometer. I would then plot my data against the graph of Planck's law and determine how closely the two fit.

Do you think that this would be a good experiment for this lab? Also do you think there are any other tools I would need? Maybe a voltage amplifier to get the Tungsten to a higher temperature? Can you think of any problems I would have?

Thanks for your help!

 

[tech99]

For my undergraduate physics lab, we are asked to spend 3 weeks (3 3-hour sessions + any time during the week if I need extra time) doing an experiment of our own choosing. The physics department will provide any experimental tools needed within reason.

I have been considering using this time to measure the intensity vs. wavelength of the light emitted from a tungsten filament at different temperatures. I would do this by focusing the emitted light through a lens then separating the wavelengths with a prism and finally detecting the intensity by wavelength with a spectrometer. I would then plot my data against the graph of Planck's law and determine how closely the two fit.

Do you think that this would be a good experiment for this lab? Also do you think there are any other tools I would need? Maybe a voltage amplifier to get the Tungsten to a higher temperature? Can you think of any problems I would have?
The lamp temperature can be set by using a variable voltage supply. How about a 12 volt halogen bulb to obtain bluish light, as you can dim it down to give IR only? You need calibrated sensors for the optical and IR spectrum. You probably cannot go very much into the IR spectrum because glass absorbs long wavelength IR. How will you measure filament temperature (apart from measuring wavelength!)? Maybe you could find the temperature by measuring the voltage and current to find its resistance and compare this with the resistance in normal operation.
Thanks for your help!

 

[Andrew774]

Is there a way that I could use a tungsten filament without the bulb/glass to avoid the infrared light being absorbed without the tungsten catching fire? Or is there another material that I could use to get a nice full Planck curve?

 

[tech99]

Is there a way that I could use a tungsten filament without the bulb/glass to avoid the infrared light being absorbed without the tungsten catching fire? Or is there another material that I could use to get a nice full Planck curve?

I think a tungsten filament will work in air up to dull red, or evn organge with short.

Is there a way that I could use a tungsten filament without the bulb/glass to avoid the infrared light being absorbed without the tungsten catching fire? Or is there another material that I could use to get a nice full Planck curve?

If you smash the glass envelope of a Tungsten bulb. I think the filament will operate in air for some time if you keep it to red or orange. You need to experiment. May I mention that I have found that glass lenses etc tend to warm up during an experiment, and then radiate IR.