|
light passing through the paper. Trim any
excess tape. 8. Tape the front end panel to the wide opening of the spectroscope housing. Make sure the seams are closed so that no light escapes through them. 9. The final step in making the spectroscope is to close off the other open rectangle except for a very narrow vertical slot. The slit can be cut from aluminum foil. It should be about one millimeter wide. Use a razor knife to make this cut. Any roughness in the cut will show up as dark streaks in the spectrum perpendicular to the slot. Cover the open rectangle on the front piece with the foil. The slit should be vertical. Temporarily hold the paper in place with tape. Calibrating the Spectroscope: 1. To obtain accurate wavelength readings with the spectroscope, it must be calibrated. This is accomplished by looking at a standard fluorescent light (Do not use a broad-spectrum fluorescent light.) 2. Lift the tape holding the slit and move the slit to the right or left until the bright green line in the display is located at 546 nanometers. Retape the slit in place. The spectroscope is calibrated. Discussion: Unlike a prism, which disperses white light into the rainbow colors through refraction, the diffraction grating used in this spectroscope disperses white light through a process called interference. The grating used in this activity consists of a transparent piece of plastic with many thousands of microscopic parallel grooves. Light passing between these grooves is dispersed into its component wavelengths and appears as parallel bands of color on the retina of the eye of the observer. Spectroscopes are important tools for astronomy. They enable astronomers to analyze starlight by providing a measure of |
the relative amounts of red and blue light a
star gives out. Knowing this, astronomers can
determine the star's temperature. They also
can deduce its chemical composition, estimate
its size, and even measure its motion toward
or away from Earth (See the activity Red Shift,
Blue Shift.) Starlight (photons) originates from the interior of a star. There, pressures are enormous and nuclear fusion is triggered. Intense radiation is produced as atoms, consisting of a nucleus surrounded by one or more electrons, collide with each other millions of times each second. The number of collisions depends upon the temperature of the gas. The higher the temperature, the greater the rate of collisions. Because of these collisions, many electrons are boosted to higher energy levels, a process called excitation. The electrons spontane-ously drop back to their original energy level. In doing so, they release energy as photons. This is what happens to the filament of an electric light bulb or to an iron bar when it is heated in a furnace. As the temperature of the filament rises, it begins to radiate reddish light. When the filament becomes much hotter, it radiates bluish light. Thus, the color it radiates is an indicator of the filament's temperature. Stars that radiate a great amount of red light are much cooler than stars that radiate a great amount of blue light. Stellar spectra therefore serve as star thermometers. Excitation of electrons can also occur if they absorb a photon of the right wavelength. This is what happens when certain materials are exposed to ultraviolet light. These materials then release new photons at different wavelengths. This is called fluorescence. One of the important applications of spectroscopes is their use for identifying chemical elements. Each element radiates light in specific wavelength combinations that are as distinctive as fingerprints. Knowing the |