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The waves are not shown to scale. Ask students, based on the illustration above, to guess which color has the longest wavelength?

The answer is red. The wavelengths of the other colors decrease in order, with violet light having the shortest wavelength. Tell students that in this hands-on lab, they will construct a simplified model of different light waves in order to determine a constant relationship between wavelength and frequency.

Hand out the procedure sheet to each group in order for them to see the instructions along with hearing them. Diagram showing how to label the tape. He or she may also share in the completion of the tasks. Note : The true wavelengths are actually measured in terms of angstroms. An angstrom is 10 -8 cm or 0. Red has a wavelength of angstroms, green has a wavelength of angstroms and violet has a wavelength of angstroms.

However, in this lab, the simple relationship among the visible light waves will be what is important. Diagram showing the cutout on the manila folder should look. Diagram showing the setup for this lab. Formative assessment and observation should be evident throughout the lesson. The worksheet, final questions during closure or a future quiz may serve as summative assessment. Direct students to write for five minutes in their journals summarizing the lab and all procedures in this lesson.

Encourage students to then share their findings and what they might have written in their journals. The general idea for this lesson plan was adapted from a lesson written by Dr. Charles W. McLaughlin which was found in Science Experiments on File. Thus violet light is bent more than red light, as shown for a prism in Figure 3b, and the light is dispersed into the same sequence of wavelengths as seen in Figure 1 and Figure 2.

Figure 3. Since the index of refraction varies with wavelength, the angles of refraction vary with wavelength. A sequence of red to violet is produced, because the index of refraction increases steadily with decreasing wavelength. Any type of wave can exhibit dispersion.

Sound waves, all types of electromagnetic waves, and water waves can be dispersed according to wavelength. Dispersion occurs whenever the speed of propagation depends on wavelength, thus separating and spreading out various wavelengths.

Dispersion may require special circumstances and can result in spectacular displays such as in the production of a rainbow. This is also true for sound, since all frequencies ordinarily travel at the same speed. If you listen to sound through a long tube, such as a vacuum cleaner hose, you can easily hear it is dispersed by interaction with the tube. Dispersion, in fact, can reveal a great deal about what the wave has encountered that disperses its wavelengths.

The dispersion of electromagnetic radiation from outer space, for example, has revealed much about what exists between the stars—the so-called empty space.

Figure 4. Part of the light falling on this water drop enters and is reflected from the back of the drop. This light is refracted and dispersed both as it enters and as it leaves the drop. Rainbows are produced by a combination of refraction and reflection. You may have noticed that you see a rainbow only when you look away from the sun. Light enters a drop of water and is reflected from the back of the drop, as shown in Figure 4.

The light is refracted both as it enters and as it leaves the drop. Since the index of refraction of water varies with wavelength, the light is dispersed, and a rainbow is observed, as shown in Figure 5a. There is no dispersion caused by reflection at the back surface, since the law of reflection does not depend on wavelength. The effect is most spectacular when the background is dark, as in stormy weather, but can also be observed in waterfalls and lawn sprinklers.

The arc of a rainbow comes from the need to be looking at a specific angle relative to the direction of the sun, as illustrated in Figure 5b. This rare event produces an arc that lies above the primary rainbow arc—see Figure 5c. Figure 5. Dispersion may produce beautiful rainbows, but it can cause problems in optical systems.

White light used to transmit messages in a fiber is dispersed, spreading out in time and eventually overlapping with other messages. Since a laser produces a nearly pure wavelength, its light experiences little dispersion, an advantage over white light for transmission of information. In contrast, dispersion of electromagnetic waves coming to us from outer space can be used to determine the amount of matter they pass through.

As with many phenomena, dispersion can be useful or a nuisance, depending on the situation and our human goals. How does a lens form an image? See how light rays are refracted by a lens.

Watch how the image changes when you adjust the focal length of the lens, move the object, move the lens, or move the screen. Figure 6. This prism will disperse the white light into a rainbow of colors. The incident angle is Skip to main content. Geometric Optics. Search for:. Dispersion: The Rainbow and Prisms Learning Objective By the end of this section, you will be able to: Explain the phenomenon of dispersion and discuss its advantages and disadvantages.