Planck's Constant from an LED

Purpose:
The purpose of this experiment is to measure the Planck's constant using different LEDs. The experiment is conducted based on the concept of  the light emitting diode and interfere constructively of light going through a diffraction grating.
Procedure:

LEDs are connected to the DC power supply and the resistance box. Adjusting a resistance box to make the LEDs on with minimum voltage across the LEDs. The voltages across are recorded.

Shining the LEDs through the diffraction grating. Another person is looking through the grating to see the interference. The distance of the grating to the LEDs and the distance of interference are recorded.

Calculation of wavelength:

Derivation of Planck's constant:

Data table:

LED	Voltage (V)	Wavelength (nm)	h (Js) *10-34	% Error (%)
red	1.56	670 ± 18	5.57 ± 1	15.9
green	1.87	551 ± 15	5.49 ± 1	17.1
blue	2.25	485 ± 14	5.82 ± 1	12.1
yellow	1.63	594 ± 14	5.20 ± 1	21.5

The slope is the value of Voltage times Wavelength.
From the slope, the Planck's constant is equal to (slope*q)/c = 5.33E-34
% error is 19.5%

Summary:
According to the purpose of this experiment, the Planck constant  was successfully measured by using the electromagnetic radiation and light emitting diode. However, the result was not accurate due on the systematic measurement of the voltage across the LEDs and the wavelengths. The wavelengths were calculated based on the spectrum of LED light through the diffraction grating. As doing the experiment, we observed that not every LED give the single color when we looked through the grating. The green LED gave a mixture of colors in the spectrum. Moreover, the relationship between the color of the LEDs (wavelength) and its potential (voltage) is inversely proportional.

Project

Pre-poposal:

The purpose of this project is we going to build a periscope which magnify an image as seen by human eyes. The idea is using a series of lenses to see an upright image through the lenses. Also, we are using some simple geometry mirrors to see the image above, forward and backward.
 

Bill of materials:

10 feet- 4'' drain pipe - $6.95
2- 4'' drain pipe 90 degree  - $ 6.04 each
duct tape - $8.28
3 convergent lenses
2 mirrors


Pictures of progress:

in progress

Active Physics Laser

Purpose: 
The purpose of this activity is to explore the concept how the laser work by investigating the difference between stimulated emission and spontaneous emission. Students will use active modern physics website to understand the light absorption and emission throughout this activity.
  

1) As shown there are fourteen excited atoms and three loose photons. The number of photons pumped into the system are twenty two, the number of photons come out of the system are five. So, we can see the total number of excited atoms, loose photons and come out photons are equal to the number of photons pumped into the system.

2) As shown in the picture, there is no preferred direction for the photon emitted during spontaneous emission.

3) No, there is a large time difference in the time emission between atoms in spontaneous emssion.

4)For each input photon when it interacts with an excited atoms, It gains one more photon oriented same direction with the input.

5) Experimentally, the effect starts occurring at pumping level 70. The picture shows the pumping level 90, the population inversion occurs.

6) In the laser, the photon emits which non-direction is the spontaneous emission.

Summary:
According to the activity, the number of photon inputted into the system are equal to the number that come out of the system and excited atoms. In the spontaneous emission, the emitted photons do not have any specific direction; although, when a photon interacts with an excited atom in the stimulated emission, it gains another photon in the same its direction. By changing level of pumping, we found that the pumping level at least 70 is required to have population inversion. If one of photons is emitted in another direction, not in the incident's direction, the photon is emitted spontaneously.

Color and Spectra

Purpose:
The purpose of this experiment is to understand how different elements can emit different certain wavelengths and identify an unknown element based on the wavelengths that element emits. This experiment is using the concept of light rays going through the grating, the colors with distinct wavelengths interfere constructively creating different colors at different positions.

Procedure:
 Using a light source, a grating filter, a 2-meters stick and a 1-meter stick to conduct this experiment. The light source is shone through a grating which located 190 cm away. Another meter stick was place beside the light source in order to measure the distance of colored spectrum. The color spectrum was seen through the grating. The distance of the color spectrum and the grating were recorded in order to calculate the wavelengths were emitted. A hydrogen light source was obtained, and the distance of the light source and color spectrum were measure as the same manner. The last part was an unknown light source given by the Professor to identify the element based on the wavelengths.

 The wavelengths were calculated based on the distance of the light source and the distance of the color spectrum.

Figure 1: Derivation of Wavelength

Figure 2: Set up

Figure 3: light spectrum of the white light

Figure 4: Light spectrum of hydrogen gas

 Figure 5: light spectrum of unknown #4

Data analysis:

 Table 1: wavelengths of visible light spectrum from white ligh

Color	L (cm) :distance of the light source	D(cm) : distance of the spectrum	d(cm) : distance between grooves	Experimental Wavelength (nm)	Actual wavelength (nm)
Red (max)	190 ± 1	73 ± 1	2*10-4	717 ± 17	750 ± 10
Yellow (middle)	190 ± 1	53.5 ± 1	2*10-4	542 ± 23	570 ± 10
Green (middle)	190 ± 1	48.5 ± 1	2*10-4	495 ± 23	510 ± 10
Blue (middle)	190 ± 1	45 ± 1	2*10-4	461 ± 23	475 ± 10
Violet (min)	190 ± 1	37 ± 1	2*10-4	382 ± 22	390 ± 10

Table 2: Wavelengths of the visible light spectrum from hydrogen light

Color	L (cm) :distance of the light source	D(cm) : distance of the spectrum	d(cm) : distance between grooves	Experimental Wavelength (nm)	Actual wavelength (nm)
Red	190 ± 1	67 ± 1	2*10-4	675 ± 23	656
Blue	190 ± 1	48.3 ± 1	2*10-4	490 ± 23	486
Violet	190 ± 1	43 ± 1	2*10-4	441 ± 22	434

 Table 3: Wavelengths of the visible light spectrum from unknown #4

Color	L (cm) :distance of the light source	D(cm) : distance of the spectrum	d(cm) : distance between grooves	Experimental Wavelength (nm)	Actual wavelength (nm)
Red	190 ± 1	59.5 ± 1	2*10-4	597 ± 23	623.4
Orange	190 ± 1	58.5 ± 1	2*10-4	588 ± 20	615.2
Yellow	190 ± 1	56 ± 1	2*10-4	565 ± 21	577
Blue	190 ± 1	49 ± 1	2*10-4	499 ±23	502.5

 Based on the wavelengths, the unknown element is Mercury. 

Figure 6: Uncertainty calculation

Summary:
According to the results, the experimental wavelengths were within reasonable. The results were within uncertainty comparing to the actual values. The relationship between the actual and experimental wavelengths was obtained in the graph shown above. That was wavelength spectrum of visible light.
According to the wavelengths of the unknown element, that was a Mercury light because the light spectrum lines matched with the Mercury spectrum most among the elements spectrum we have.
There were some uncertainty in the results. The uncertainty could be from the distance of the light spectrum when we saw through the grating, the uncertainty in the measurement, the spectrum did not appear clearly.