Finding Planck's Constant with LEDs

[Paul37]

Homework Statement

I am trying to prove Planck's constant using LEDs. So far I have measured several LED's wavelengths using a spectrometer and from this their frequency. This will be f in the equation h = E/f. For E I put the LEDs in a forward biased circuit and am trying to use the equation E = qV to find E so I can therefore find Planck's constant. My question is which value do I use for V? The minimum voltage needed to produce a current in the circuit or the voltage the circuit eventually tends to.

Homework Equations

E=hf
E=qV

Thanks very much in advance.

Also, do you know of any related experiments that I could do concerning this sort of area. I was going to find the wavelength of a UV LED and find its energy by a different method (not going to look at a UV LED through a spectrometer) but I wasn't sure exactly how to do that.

 

[jbsteele]

The Attempt at a SolutionFor the first question, you should use the voltage that the circuit eventually tends to. This is because the voltage that is needed to produce a current in the circuit will only give you the minimum energy required for the LED to operate, but not the actual energy of the LED. Therefore, you should use the voltage that the circuit eventually tends to in order to get the most accurate value of E. As for the second question, you can measure the energy of a UV LED by measuring the energy emitted by it when it is placed in a photovoltaic cell. The amount of energy measured will correspond to the energy of the UV LED.