The purpose of this experiment is to determine the planck's constant using the combination of electromagnetic radiation and conduction in solids, specifically p-n junction, concepts.
This experiment was conducted using a yellow and blue LED, a power supply, 2 wires, a 150 ohm resistor, and a multimeter. The power supply was connected in series with the LED and the resistor. A supplied voltage was given from the power supply, and the voltage through the LED was measured using the multimeter. The voltage drop was computed by subtracting the voltage across the LED from the supply voltage. A wavelength vs. c/E was constructed in order to determine the experimentally determined planck's constant.
Figure 1: Blue and yellow light emitted from the LED when a power supply was given
Data and Analysis
Table 1: Data including the voltages and wavelength
Color
|
Wavelength (nm)
|
Vsupply (V)
|
VLED (V)
|
Vdrop (V)
|
Yellow
|
590 ± 10
|
3.05 ± 0.01
|
1.95 ± 0.01
|
1.10 ± 0.01
|
Blue
|
450 ± 10
|
3.05 ± 0.01
|
2.76 ± 0.01
|
0.29 ± 0.01
|
4.50 ± 0.01
|
3.00 ± 0.01
|
1.50 ± 0.01
|
Graph 1: Wavelength vs. c/E without taking uncertainty into account
Graph 2: Wavelength vs. c/E with uncertainty
Table 2: Comparison of the value of the planck's constant
Experimental h
|
Actual h
|
% error (%)
|
5 x 10-34
|
6.63 x 10-34
|
24.6
|
Conclusion
According to the graph 1, the slope is determined to be 5x10-34, which was the experimentally found planck's constant. However, the result was not very accurate since not enough data was collected in order to get a greater precision in the measurements. In addition, the wavelength were not accurate since these wavelengths were estimated based on the closest spectrum of light each LED emitted. These error contributed to total percent error of 24.6%. Yet, the value appeared to have same order of magnitude with the planck's constant. When the graph was reconstructed by including uncertainty (590nm became 600nm, and 450nm became 440 nm), the slope became 6x10-34 as shown in graph 2. This showed that more trials could lower the uncertainty and gave the planck's constant closer to its actual value.
