Spectroscopes

Most light is composed of several different colors. We can easily observe this by refracting white light (e.g. sunlight) through a glass prism.

To separate the colors we will use a spectroscope rather than a prism. A spectroscope works by using diffraction to separate the different colors of light. Inside the spectroscope you will see each of the colors that are present in a light source. For example if you look at white light through a spectroscope, you will see all of the colors of the rainbow. Other light sources will have fewer colors. This display of color is called a spectrum.

Some spectroscopes provide scales directly in eV. Others show measurements in nanometers (nm) or Ångstroms (Å). If yours uses one of these units, recording your observations on a scale like the one below will enable you to determine the energy value in eV directly.

Record your observations of spectra using the scales provided in Solids and Light, Activity 2.

How to Use a Spectroscope
The following directions apply to the plastic "Project STAR" spectrometer (or spectroscope) you have been provided with. If you are using something else, follow the same basic procedure however details may differ.

1. Firstly to ensure your spectroscope is properly adjusted, set up a white light source. A good white light source is the incandescent bulb you used in the previous tutorial. Dim the lights of the room so that the light patterns may be seen. The room, however, should be lighted enough for the energy scale to be seen.
2. Hold the spectroscope with the eyepiece toward you and the small square opening at the other end close to the light source.
3. If you look into the eyepiece you should see a small vertical rectangular slit. To ensure that the light patterns are clearly visible, position the vertical slit of the spectrometer so that it is directly facing the light source and, if possible, hold the spectrometer less than a foot away from the light source.
4. Without moving the spectroscope, look to the left of the slit and you should see an illuminated scale like the one shown above. If the scale appears to the right, you have the spectroscope (and the scale) upside down.
5. While still looking at the scale carefully rotate the eyepiece until you see a continuous spectrum within the scale.

At this point you should be seeing something like this: