Experiment 16: Determining Planck's Constant

Introduction:
In this experiment, 4 different LEDs were used in order to make measurements to experimentally determine the value of Planck's constant, 6.626 * 10^-34 J*s.

Data:
Setup:

Power supply setup for LEDs

Initially, we measured the size of the continuous spectra and voltage of a yellow, red, blue, and green LED.



Yellow:

Yellow LED continuous spectra.

Red:

Red LED continuous spectra.

Blue:

Blue LED continuous spectra.

Voltmeter reading of 2.66V for blue LED.

Green:

Green LED continuous spectra.

Voltmeter reading of 2.82V for green LED.

Measurements made for LEDs.

A white LED was then investigated to see its continuous spectra and gather a voltage reading.

White:

White LED continuous spectra.

Voltmeter reading of 2.72V for white LED.

Calculations:

Calculations made for each LED.

Using the equation E=hf, where c=f*lambda, we can rewrite E=hf as lambda = hc/E. We notice that plotting our wavelength vs. voltage, we get our slope to be our experimental planck's constant value. 

Conclusion:
We notice that by graphing, we get a planck's constant value of 1.959 *10^-34, which gives us a percent error of 70.43%, but by calculating by hand, we get a planck's constant value of 6.849 * 10^-34, which gives us a percent error of 3.37%. This tells us that the use of more LEDs could give us much better results for an experimental planck's constant by graphical methods.