The purpose of this lab is to be able to determine the value of the Planck's constant experimentally. This could be done by measuring the energy of different colors of LED and determine the wavelength for each. In this lab, the blue and yellow LED are used to determine the Planck's Constant.
Experimental
Simple circuit is built as follow and the voltage is measured
 |
| Spectrum of Blue LED |
Based on the experiment ,the data obtained is as follow:
|
Color
|
Wavelength
|
Energy
|
|
Blue
|
450 nm
|
1.95 eV
|
|
Yellow
|
590 nm
|
2.76 eV
|
We can find the relation of lambda being lambda = hc/E
Which also mean that hc is our slope of the graph.
Since c is constant being 3*10^8 m/s , we can find h
h = m / c = 1*10^-25 / 3*10^8 = 3.33*10^-34
The theoretical value for Planck's Constant is 6.628 *10^-34 which mean our percent error is 50%.
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