Color and Spectra Lab

Part 1: The Spectrum of White Light

We began by using a light box and placing it a distance of 1.96+/-0.3 m away from the diffraction grating. A rainbow of colors could be observed through the grating.

The colors were blurry if the lights were on. However, the image became clearer once the lights were shut down. The closest color to the light source was violet, followed by blue, green, a slit of yellow and finally a red color.


Part 2: Measuring Wavelength - Theory

Part 3: Measuring Wavelength - Experimental



The following relationships will help to find the wavelenght of color as seen through the grating;

The grating used for this experiment had 500 groves per mm. This means that the distance, d, between the grove was found to be  2*10^-6 m.

The distance between the light source and the edge of each color were:

Violet: 36.7 +/- 0.5 cm
Blue: 45.5 +/- 0.5 cm
Green: 53.7 +/- 0.5cm
Red: 83.5 +/- 0.5 cm

The distance between the light source and the middle of each major color were:

Violet/Blue: 45.5 +/- 0.5 cm
Green: 53.7 +/- 0.5 cm
Red: 70.3 +/- 0.5 cm

All this values represent D in the equation.
L = 1.96 +/- 0.3 m
d = 2*10^-6 m

λ violet  = 368 +/- 5 nm              Shortest wavelength

λ blue = 460 +/- 4 nm

λ green = 540 +/- 5 nm

λ red = 784 +/- 4 nm                   Longest wavelength

Part 4: Spectra of a Single Element 

We took a hydrogen gas tube which substituted the light box, and then we did the same procedure as in the previous part.

 

We came up with the following data and the respective percent errors based on the calculated wavelengths from Part 2.

Identifying an unknown gas

Once we knew how to measure wavelengths of light through spectrum lines, we could now be able to identify an unknown gas from the light it emitted.

We were given unknown sample number 3:

 

The distances, D, between the gas tube and each spectrum line were the following:

Dviolet = 0.441 +/- 0.002 m

Dcyan = 0.500 +/- 0.002 m

D red = 0.693 +/- 0.002 m

Based on spectrum diagrams for different gases, we concluded that the closest gas whose wavelengths were close to the unknown, was Xenon gas.