Planck Constant:
This experiment will require a cell, ammeter, voltmeter, resistor and LED lights of varying colours/wavelengths.
1) Attach an LED to the circuit using a flying lead to complete the circuit, and start with the resistor on maximum resistance.
2) Using some sort of tube, look at the light on the LED to see when the LED first starts to emit light. Simultaneously, turn the resistor down very slowly.
3) When the light first begins to be emitted, record the corresponding voltage and current for that wavelength. This is the "threshold frequency".
4) Repeat this fro LEDs with varying wavelengths.
5) Use the data recorded to plot a graph of Voltage (threshold) no the y-axis and 1/wavelength on the x axis.
The gradient of the graph is equal to V/Wavlength, since V = eV, we can rearrange this:
eV = hc/wavlength
V = hc/ wavelength*e
Now rearrange into the form y = mx + c:
V = hc/e * 1/wavelength
So using the graph we can calculate the planck constant (estimate):
Planck constant = gradient * 1/wavelength