Grade Level: 6th – 8th grade
Subject Matter: Physical Science
National Standards: NS.5-8.1, NS.5-8.2
A Recipe for Slime
One lamp fixture
One incandescent light bulb - 40 watts
One compact fluorescent light bulb - 7 watts
One ultraviolet light or black light bulb - 40 watts
One infrared or red heat bulb - 40 watts. Available at pet stores.
Glow-in-the-dark stars, all in the same size – three for each student or group of students
One camera – or students may bring their own.
Phosphorescence – A phenomenon in which an object absorbs light energy and gradually releases it, even after the original light source is removed.
Visible Light – The only type of light waves that humans are capable of seeing, ranging from red to violet and including all the colors of the rainbow.
Ultraviolet (UV) Light – A type of light that is invisible to humans and is a significant component of sunlight.
Infrared (IR) Light – A type of light that can be experienced in the form of heat. Although we cannot see infrared without the use of a special filter, living and non-living things emit infrared light.
Incandescence - The emission of visible light from a hot body due to its temperature. In an incandescent light bulb, a filament, or thin wire, is heated to a temperature at which a small fraction of the radiation falls in the visible spectrum. But most of the radiation is emitted in the infrared part of the spectrum, which means that incandescent lights are relatively inefficient.
Fluorescence - The emission of light by a substance that has absorbed light of a different wavelength. In a fluorescent light bulb, electricity is used to excite a small amount of mercury vapor or gas. The excited mercury atoms produce ultraviolet light that then causes a phospher to fluorese, producing visible light. A fluorescent light bulb converts electrical power into useful light more efficiently than an incandescent bulb.
1. Begin the lesson by having students watch the Science Friday video, “A Recipe For Slime.” Begin a discussion with the students on how and why some objects are able to glow in the dark. Ask students if they think that different types of light will affect how well a phosphorescent object will glow.
2. Show students four different light sources: an incandescent light bulb, a fluorescent light bulb, an infrared light bulb and an ultraviolet light bulb. Warn students not to look at the infrared or ultraviolet light bulbs once they are turned on. Review with students the differences between each type of light, and ask them which type of light they think will cause a phosphorescent object to glow the brightest. Tell students they will conduct an experiment to test their theories.
3. Hand out the bags/containers of glow-in-the-dark stars to each student or group of students, making sure that the stars remain enclosed. Tell students not to remove the stars from the closed containers/bags until it is time to conduct the experiment. Why is this important?
4. Close the curtains/shades and turn off the lights in the room. Make sure that there is enough indirect light for students to see. Have students remove one star from the container, while you shine the infrared light on the object at a distance of two inches for 20 seconds. Remind students not to look directly at the infrared light bulb once it is turned on.
5. Have students ready with a camera to take a picture of the star after the 20 seconds are up. Make sure students take a picture of the object immediately after the light is turned off at a distance of six inches and with the flash OFF. Why is it important to have the flash off?
6. Repeat the experiment three more times, using another star from the container for each light source (incandescent, fluorescent, and ultraviolet). Remind students not to look directly at the ultraviolet light bulb once it is turned on. Have students write down the order of the light sources used, so that they will be able to differentiate each picture later.
7. Depending on the type of camera, have students compare each picture by either viewing them on the camera, downloading pictures onto a computer, or developing the pictures. Which light source caused the star to glow the brightest?
8. Have students place the images in the order of brightest to least bright. Discuss with students why they think one particular light source worked better than others.
When light hits normal, everyday objects, it usually is either absorbed or immediately reflected. However, when light hits a phosphorescent object, the energy is absorbed and stored or “charged.” The phosphorescent object will hold onto the energy and gradually re-emit the energy as light. (The color it glows depends on the type of material.) Because the light slowly is being released, it appears to glow even after the light source is turned off.
• Instead of testing for intensity of light emitted, how can students test the persistence of light emitted?
• Would the results be the same if a different phosphorescent material were used?
• How does this experiment relate to the electromagnetic spectrum? Are there other types of light waves that also could be tested?
• What are some practical or important uses for phosphorescent objects?
Explore fluorescence by examining classroom or household items under a black or ultraviolet light, taking care not to look directly at the light source once it is turned on. Have students conduct an investigation, based on their observations, to determine the differences between fluorescence and phosphorescence.