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Paul37

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**Planck constant "V" in E=qV question**

1. 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.

2. 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.