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.