After this activity, students should be able to:

• Understand the phenomenon of refraction — that when light travels across the border of two transparent media (such as air, glass, Lucite, etc.), the path of light bends.
• Understand the basic concepts of how a magnifying glass works.
• Understand that light is made up of waves, and that waves at different wavelengths create different colors.
• Understand that a prism sorts a light beam into its various wavelengths, appearing as a rainbow of colored light.
• Explain that there are also waves that cannot be seen by the human eye that affect our daily lives. For example, we wear sunscreen and sunglasses to protect our skin and eyes from ultraviolet waves.
• Understand how polarized light works.
• Explain what is happening with polarized sunglasses.

Diffuse light energy from the sun is concentrated into a focal point by a magnifying glass. click for copyright

Light is amazing! It is a form of energy that can bend and bounce, and it comes in all different colors. What do you call it when light bounces off something? It is called reflection. And, that is what is happening when we look at our reflection in the mirror — light is bouncing back at us from the mirror. When light bends through something, such as water, it is called refraction. Have you ever been in a swimming pool and seen someone in the water look cut off at the surface of the water? What you are seeing is due to refraction. Have you ever played with a prism? Well, we are going to look at one today to see another form of bending, or refraction, of light. How about a magnifying glass? Well, that is a way light energy waves are refracted to make an image seem larger.

Demonstration idea: If a slinky is available, use it to show how waves vibrate in different wavelengths. Explain how the different "wavelengths" correspond to different colors. Use the slinky to show the class that waves can vibrate in any plane (vertical, horizontal or any angle in between). White light contains all of the wavelengths of the visible light spectrum (see Figure 1) and all of the possible angles shown by the slinky.

Who remembers the colors of the rainbow? Have you ever noticed that the colors of a rainbow are always in exactly the same order? Show students the Visible Light Spectrum visual aid (the same as Figure 1). Inform them that ROY G BIV is a good way (acronym) to remember the order of the colors of the rainbow. In addition to these visible light waves, there are many more waves of light that cannot be seen with the human eye! Show students the Electromagnetic Spectrum visual aid. Ultraviolet (UV) waves are even shorter than violet waves and infrared waves are longer than red waves. We can only see the colors in the middle, the visible light spectrum.

Figure 1. The colors and wavelengths of the visible light spectrum. Note the order of the colors (ROYGBIV), and their varying wavelengths. Red is the longest wavelength, violet the shortest. click for copyright

Do you know which of these light energy waves causes sunburn and can hurt our eyes. (Answer: Ultraviolet light waves.) What do we do to protect ourselves from UV rays? (We wear hats, sunglasses and sunscreen.)

How does light energy affect us? Our eyes are sensitive to the brilliance of sunshine. Ultraviolet light penetrates clouds and fog, and is reflected back at us from snow and water. If unprotected from the ultraviolet waves, our eyes can be burned and/or permanently damaged. We can reduce this risk by wearing a high-quality pair of polarized sunglasses designed by engineers to limit the amount of ultraviolet light reaching our eyes.

click for copyright

How do polarized sunglasses work? Well, if we have a piece of paper containing a vertical (up and down) slit, what light do you think would pass through? Only waves in the vertical plane would pass through. The same applies for a horizontal slit and horizontal waves. When light reflects off water, all of the waves are oriented horizontally. This causes the intense glare off the water's surface you may have noticed. Polarized sunglasses work much like a letter going in to a mail box slot. If the letter is not positioned correctly then it cannot go into the mail box.

What do you predict would happen to light trying to pass through two polarized lenses oriented perpendicular to each other? (Answer: Wait for the hands-on activity to find out for yourself!)

Years ago (even in prehistoric times), Inuit people (also called Eskimos) who live in the snowy Arctic carved goggles of wood or bone with a narrow horizontal slit across the front. See a photograph of an Inuit wearing his snow goggles at the Houston North Gallery website, http://www.houston-north-gallery.ns.ca/Sugluk/pictures_of%20Inuit_8.htm. This allowed them to better see in "white out" snow conditions when light was coming from every direction and all contours were missing. How do you think this worked? How is this similar or dissimilar to the polarized sunglasses? (Answers: This is the same way that polarized sunglasses work. The horizontal slits only allowed part of the light waves, the horizontal ones, through to the Inuit's eyes.)

In addition to designing sunglasses that protect your eyes, engineers apply their knowledge of polarized light in laser applications, electron microscope imaging and medical imaging techniques.

Today, you will work in small teams and rotate through four stations where you will examine light energy behavior in more detail: refraction, magnification, prisms and polarization.

Before the Activity

With the Students

Station 1: Bending Light

1. Fill the bowl half full with water. Make sure the bowl is deep enough to demonstrate refraction.
2. Have students place the ruler (or pencil or popsicle stick) straight up in the water and slowly lower it towards horizontal.
3. Have students record their observations and answer the questions on the worksheet.

What's happening? The ruler appears to be bent at the surface between the water and the air. As the ruler approaches horizontal, the bend appears to increase. This is because when light travels across the border of two transparent media (such as air, glass, Lucite, etc.), the path of light bends. This phenomenon is called refraction.

Engineering connection: Lighting engineers are interested in the properties of light, especially natural daylight. Energy engineers study light properties to determine the best type of windows to put in a building. They are concerned with how much visible light can pass through the window and where it will land in the space, as well as how much illumination and energy the light adds to the space. Glass with high visible transmittance allows much light into the space; glass with high solar heat gain coefficients allows much energy to enter the space.

Station 2: Lens and Light

1. Have the students examine the pictures and words through the magnifying glass. What happens if they hold the magnifying glass at different distances?
2. Have students record their observations and answer the questions on the worksheet.

What's happening? Some students may notice that images flip when you hold the magnifying glass at a certain distance. This is because the image converges at a focal point. When the image diverges beyond this point, its orientation is flipped (see Figure 2).

Figure 2. An image seen through a magnifying glass held at a distance further away than the focal point appears to be upside down. click for copyright

Engineering connection: Engineers use their knowledge of light energy and lenses as they design prescription eye glasses, reading glasses, cameras, contact lenses, eye surgery equipment and techniques, solar energy collection equipment, telescopes, microscopes, satellites, optics and lasers. Using a lens as a light-collecting tool enables engineers and scientists to take photographs in dark rooms and invent other devices to improve our vision of the very tiny, very far away, and locations unsuitable for human life (in hot volcanoes, deep the ocean, in outer space).

Figure 3. A prism "sorts" light into various colors (ROYGBIV), each with their respective wavelengths. click for copyright

Station 3: Prism Rainbows

1. Shine light through the prism to create a rainbow (see Figure 3). The colors are referred to as the visible spectrum.
2. White light contains all of the colors in the visible spectrum.
3. Have students record their observations when light passes through the prism and answer the questions on the worksheet.

What's happening? The shorter the wavelength, the more that light is bent or refracted by the prism. In a similar situation, light passing through water (or water droplets in the air) can create a rainbow.

Engineering connection: Prisms are used in all sorts of engineered devices. Binoculars use pairs of prisms to lengthen the path of light so that far-away objects appear closer, and also to turn the image, which is reflected off a mirror upside down. Prisms are also used to focus light rays in medical equipment and general lighting applications.

Figure 4. Setup for Station 4: Polarized Light. click for copyright

Station 4: Polarized Light

1. Have one student put on a pair of polarized sunglasses and hold the plastic polarized film in front of him/her. Then, slowly rotate the film in either direction.
2. What do you notice when the film is straight up and down? What do you notice when the film is rotated 90 degrees?
3. Have students record their observations and answer the questions on the worksheet.

What's happening? Light particles travel in waves. Every light wavelength in the visible spectrum corresponds to a specific color (see Figure 1). White light contains all the visible wavelengths. A polarizing filter consists of many parallel tiny openings. Light waves traveling in the same plane as the openings pass through the filter, while all other waves of light are blocked (see Figure 5). Light that has passed through the filter is considered "polarized" — its light waves travel in approximately parallel planes. The sunglasses' lenses and the plastic film are both polarizing filters. When the plastic film is rotated to only allow light traveling in a horizontal plane to pass through, fewer and fewer light waves can pass. When the two filters are oriented perpendicular to each other, no light can pass. When the polarized lenses and the polarized film are oriented at 90 degrees, the lenses become opaque.

Figure 5. Light waves traveling in the same plane as the openings in a polarizing filter pass through it, while all other waves of light are blocked. click for copyright

Engineering connection: Engineers apply their knowledge of polarized light in laser applications, electron microscope imaging and medical imaging techniques. They also create sunglasses and camera filters that reduce the glare/reflections from the sun. Polarized light is also used to determine how forces impact machine parts. A copy of the part is made in plastic and viewed under a polarized light as a force is applied. Color bands appear where force is being transferred through the object.

Class Discussion

Conclude the activity by bringing the class together for a discussion and review of their worksheet observations. Review the "What's happening?" and "Engineering connection" information provided in the Procedure section. Conduct the post-activity assessment activities as described in the Assessment section.

These stations could also be conducted as class demonstrations.

If students are not familiar with the visible electromagnetic spectrum, show them the attached Visible Light Spectrum so they can note the order of colors refracted through the prism (ROYGBIV).

The Inuit (also called Eskimos) of the Arctic invented sun goggles by cutting slits out of bone, wood or ivory. These native peoples used natural materials to prevent snow blindness and protect their eyes from the glaring bright light reflecting from water, snow and ice. Have students make their own arctic sunglasses. Follow instructions at NASA's Snow Goggles and Limiting Sunlight website,http://solarsystem.nasa.gov/educ/docs/Snow_Goggles.pdf.

Have the students evaluate the difference between convex and concave lenses. These lenses have different types of focal points, and the images in the lenses look different.

Have the students research the optics of the Hubble Space Telescope. This huge lens orbits about 600 km (375 miles) above the surface of the Earth. It completes one orbit around the Earth every 97 minutes. The Hubble weighs about 11,000 kg (24,000 lbs) on Earth. It is 13.2 meters (43.5 ft) long with a maximum diameter of 4.2 meters (14 ft). As with most telescopes, it is its light collecting power that makes it so effective. It has two mirrors, one is 2 meters (7 ft) wide. Start your research at the NASA (National Aeronautics and Space Administration) website, http://hubble.nasa.gov/index.php

Have the students conduct a library or Internet search to learn more about wavelengths. What wavelengths are longer and shorter than the visible spectrum wavelengths? For example, longer than the red wavelengths are invisible infrared (~750 nanometers to 1 millimeter in wavelength), microwaves (1 millimeter to 1 meter in wavelength) and short-wave radio (10-20 meters in wavelength) wavelengths. Provide examples of how engineers have used their understanding of the properties of these invisible wavelengths to create equipment and instruments useful in our everyday lives.

Dictionary.com. Lexico Publishing Group, LLC. Accessed September 22, 2005. (Source of some vocabulary definitions, with some adaptation.) http://www.dictionary.com/

The Electromagnetic Spectrum. Updated August 8, 2003. IMAGERS (Interactive Multimedia Adventures for Grade School Education Using Remote Sensing), GSFC Laboratory for Terrestrial Physics, NASA. Accessed September 22, 2005. http://imagers.gsfc.nasa.gov/ems/ems.html

Polarized Light, Light and Optics, Patterns in Nature. Updated December 14, 1999. Department of Physics and Astronomy, Arizona State University, Tempe, AZ. Accessed September 28, 2005. (Good explanation and graphics) http://acept.la.asu.edu/PiN/rdg/polarize/polarize.shtml