Experiment: Planck’s constant form an LED

The purpose of this experiment is to experimentally determine Plack’s constant by an LED.

The equation used was qV=hc/λ. Solving for Planck’s constant, we get:  h = qVλ/c

Procedure:

We built the setup above to measure the voltage of the LED of various colors when it is dimmest.  In order to make the LED dim, we used varying amount of resistances.  To determine wavelength used a previous method in the color and spectra experiment.

Data:

LED	Voltage(V)	D(cm)	L(cm)	λ(nm)	h (Js)	% error
Red	1.43	28.5±1	86±1	629	4.80±0.20x10^ -34	27.6
Yellow	1.59	26.5±1	86±1	589	4.99±0.23x10^ -34	24.7
Green	1.92	23.5±1	86±1	527	5.40±0.27x10^ -34	18.6
Blue	2.00	22±1	86±1	496	5.27±0.31x10^ -34	20.3

Analysis:

The closest to the actual value of Planck’s constant of 6.62x10^-34 was the green LED with 5.40±0.27x10^ -34.  This large error was due to the low voltage read on the meter because of our set up.