A spectroscope is a device that can be used to look at the group of wavelengths of light given off by an element. All elements give off a limited number of wavelengths when they are heated and changed into gas. Each element always gives off the same group of wavelengths. This group is called the emission spectrum of the element.
White light is a combination of different colors (ROYGBIV). The spectroscope that the students will build allows them to see the separation of incoming light (through the slit) into its component colors, forming a light spectrum (rainbow). Red light has a lower frequency (longer wavelength) than blue light. Diffraction gratings contain thousands of microscopic grooves, which cause light waves to bend (longer waves bend more). Different types of light sources emit different combinations of colors and these differences are revealed when the white light "mix" is sorted into a spectrum.
Besides creating interesting color patterns a spectroscope can be used to identify different sources of light. (See the links for additional activities using the spectroscope).
In the visible wavelengths of the electromagnetic spectrum, red, with the longest wavelength, is diffracted most; and violet, with the shortest wavelength, is diffracted least. Because each color is diffracted a different amount, each color bends at a different angle. The result is
a separation of white light into the seven major colors of the spectrum or rainbow.
A good way to remember these colors in order is the name Roy G. Biv. Each letter begins the name of a color: red, orange, yellow, green, blue, indigo, and violet.
When atoms of different materials are excited by an electric current or other source of energy, they glow with a unique spectrum. Atoms of different elements have different colors in their spectra. These characteristic color patterns represent specific atoms, just as fingerprints serve to identify different people.
A diffraction grating acts like a prism, spreading light into its component colors. The light that you see from a light source is the sum of all these colors. Each color corresponds to a different frequency of light. The diffraction grating sorts light by frequency, with violet light (the highest frequency of visible light) at one end of the spectrum and red light (the lowest frequency of visible light) at the other.
When atoms in a dilute gas (like the mercury vapor in a mercury street light) radiate light, the light can be seen through a diffraction grating as a line spectrum, made up of bright lines of color. Each line in the spectrum of such a gas corresponds to one frequency of light emission, and is produced by an electron changing energy levels in the atom.
In solids, liquids, and densely packed gases, the situation is not so simple. As an atom emits light, it collides with other atoms. This changes the frequency of the light it emits. That's why solids, liquids, and dense gases have broad bands of light in their spectra.
