The spectrometer

To obtain a pure spectrum (the different colours separated without overlap) we use a spectrometer. It has three main parts:

1. Collimator: a light source in front of a slit whose width can be adjusted by a screw. The slit is located at the focal point of a convex lens, so that parallel rays leave the collimator.
2. Turntable carrying a prism. The prism is set at the position of minimum deviation for the light being studied. At this position the spectrum is sharpest and brightest.
3. Telescope consisting of two convex lenses (objective and eyepiece). The objective focuses all rays of the same colour at one point of its focal plane, giving a sharp image of the slit for each wavelength (each is a "line"). The eyepiece magnifies these images.

• Because a spectrometer can also be used for infrared and ultraviolet if suitable materials and detectors are used, it decomposes light into its components, visible and invisible.
• Astronomers use spectrometers to find the composition and even the temperature of stars and their gases, because each element has its own characteristic lines.