Procedure - Introduction

Record all observations and answers to questions in your lab notebook.

The figure here shows the Project STAR Spectrometer. Hold the spectrometer so that you can read the labels on its top surface. The narrow end of the spectrometer (at the bottom) holds the diffraction grating which disperses the light into its component colours. The wide end (at the top) holds a piece of plastic film that serves two functions:

1. At the right (inside the small square opening in the front) is a clear slit through which light enters the spectrometer.
2. The rest of the film (the part visible through the wide opening in the front) contains a calibrated scale that lets you record the wavelengths of interesting features in the spectra you observe.

To use the spectrometer, hold it so that your eye is looking through the grating in the narrow end. You should be able to see two rows of calibration marks and numbers. Pay attention to the lower row which gives the wavelength (in nanometers, or nm) of the light in the spectrum that appears above it.

To observe a spectrum, aim the spectrometer slit (that is at the front, right-hand side) to the source of light you want to examine while looking through the spectrometer. (This is the most counter-intuitive part of the whole procedure. Most people are tempted to just aim the middle of the spectrometer of the light source. Aim the right side instead.) When you have the spectrometer aimed properly, a spectrum of the light source should appear above the wavelength scale.

It will take some practice to use the spectrometer. If you wear glasses, it is best to keep your glasses on. However, you may want to cup your hand around the eyepiece to block out as much stray light as possible.

At the back of the lab will be a number of demonstration spectrometers. During the period take some time to examine them.

Acknowledgements: This lab is has parts based on materials and ideas from Project STAR (Harvard University), Boston University and Yale University.