Chapter 17 :LIGHT

What is light? Light is something that allows us to see objects. Light: is a form of energy that travel in waves. Light is a form of energy just like sound. however, unlike sound, light can travel through empty space. All waves carry energy. When the waves reach an object, some of the energy can be absorbed by that object. For example: taking a picture with a camera. Engage Activity: Direct students to look a wall chart of teacher’s choice and focus on it. Then turn off the lights, making the room as dark as possible. Ask how clear is the chart you were looking at? Turn the lights back on. Have students discuss why it was hard to see? Allow for responses. What else do you see in the room? What you really see is light bouncing off … the print on the chart, the walls, the tables, the chairs, etc. You can only see objects if they reflect light . If possible, play Color is Muted Light from Bill Nye’s classroom edition DVD LIGHT AND COLOR. Explain: Distribute a light graphic organizer (LGO) for students to write light facts as the exploration of light and its properties continues. Ask: What is light? Light is something that allows us to see objects. (Add to Light Graphic Organizer) Has light helped us do work? Does light create change? Is light a form of energy? Yes, Light is a type of energy. (Add to LGO) How does it work? Explore with the Beam of Light activity: Let’s take a closer look at a beam of light. Remind students that it is important never to look directly at any source of light, because it could damage their eyes. Shine a flashlight at the ceiling. Ask is light passing through air? Yes. Why can’t you see a beam of light in the air? Light is invisible just like the air. So we’ll follow these steps to observe a light beam : Ask for a volunteer from each group (about seven). Give one volunteer a flashlight. Put a small amount of talcum powder in the palm of each of the other volunteers’ hands. Line up these volunteers in pairs facing each other in a straight line with their palms extended holding the powder. Direct the volunteer with the flashlight to shine the flashlight just below the row of hands. Turn off the lights. The darker the room, the more easily the beam can be seen. Tell the participants to observe while the volunteers with powder clap their hands. Ask. Can you see the light beam? Why? (The moving particles of light are reflecting off the talcum powder in the air. Light is a type of energy (Add to LGO) produced by the vibration of electrically charged particles. Go to SF Pearson SuccessNet Video # 109. We’ll learn more about light by exploring light’s properties.

Properties of Light Light energy that strikes a film in a camera causes a chemical change, enabling a picture to be made. Light is a small part of a range of energy known as the “ electromagnetic spectrum”. The waves that make it up differ in frequency. “Visible Light” a part of the spectrum that a human eye can see . “ Radio waves “ have lower frequencies than visible light waves. “ X-rays” have higher frequencies. Engage: What kind of path did the light from the flashlight take in the previous activity? Then demonstrate the following with a volunteer: From a distance of about five meters, point the flashlight in its off position at the board. Have a new volunteer draw a big X on the board where he / she predicts the flashlight beam will hit. Then turn on the flashlight. Observe the beam. What happened? Gr. 3 Physical Science AIMS activity: Flashlight Findings pp. 177-182. Explain: (Add to LGO) Light travels in a straight path. Gr. 3 SF p. 371 Then repeat except this time have a volunteer place a thick piece of cardboard (or some other kind of opaque object ) in front of the beam. What happened this time? The light rays are blocked, and the cardboard casts a shadow. (Add to LGO) Light doesn’t travel through all objects. The cardboard absorbed the light rays. Absorbed light is converted into some other form, such as thermal energy. Can someone explain why most car owners prefer a light color car interior versus a black interior? What kind of energy is light converted to in this example? (heat) Add to LGO. Light can be absorbed and changed to heat. Extension: If available, play Bill Nye’s Classroom Edition DVD LIGHT AND COLOR. Go to Watch Program Section: Science Standards Clips, Clip 3 Light can be absorbed and changed to heat.

Properties of Light Waves with higher frequencies carry more energy than waves with lower frequencies . High energy waves pass through matter more easily. Example, light doesn’t pass through your body. But other forms of wave ( ex. X rays),do, at least partially. When a dentist take x-ray image of your teeth ( you hold a piece of film in your teeth & the dentist points an x-ray machine at your jaw. Engage: What kind of path did the light from the flashlight take in the previous activity? Then demonstrate the following with a volunteer: From a distance of about five meters, point the flashlight in its off position at the board. Have a new volunteer draw a big X on the board where he / she predicts the flashlight beam will hit. Then turn on the flashlight. Observe the beam. What happened? Gr. 3 Physical Science AIMS activity: Flashlight Findings pp. 177-182. Explain: (Add to LGO) Light travels in a straight path. Gr. 3 SF p. 371 Then repeat except this time have a volunteer place a thick piece of cardboard (or some other kind of opaque object ) in front of the beam. What happened this time? The light rays are blocked, and the cardboard casts a shadow. (Add to LGO) Light doesn’t travel through all objects. The cardboard absorbed the light rays. Absorbed light is converted into some other form, such as thermal energy. Can someone explain why most car owners prefer a light color car interior versus a black interior? What kind of energy is light converted to in this example? (heat) Add to LGO. Light can be absorbed and changed to heat. Extension: If available, play Bill Nye’s Classroom Edition DVD LIGHT AND COLOR. Go to Watch Program Section: Science Standards Clips, Clip 3 Light can be absorbed and changed to heat.

Properties of Light Did you notice that your teeth are white on the x-ray, but everything else is dark?! When x-rays pass through your jaw, your teeth absorb more of the x-ray energy than the rest of your mouth does. The result is that different amounts of energy reach the film in different places. On the film the x-ray energy causes changes that can be seen. Engage: What kind of path did the light from the flashlight take in the previous activity? Then demonstrate the following with a volunteer: From a distance of about five meters, point the flashlight in its off position at the board. Have a new volunteer draw a big X on the board where he / she predicts the flashlight beam will hit. Then turn on the flashlight. Observe the beam. What happened? Gr. 3 Physical Science AIMS activity: Flashlight Findings pp. 177-182. Explain: (Add to LGO) Light travels in a straight path. Gr. 3 SF p. 371 Then repeat except this time have a volunteer place a thick piece of cardboard (or some other kind of opaque object ) in front of the beam. What happened this time? The light rays are blocked, and the cardboard casts a shadow. (Add to LGO) Light doesn’t travel through all objects. The cardboard absorbed the light rays. Absorbed light is converted into some other form, such as thermal energy. Can someone explain why most car owners prefer a light color car interior versus a black interior? What kind of energy is light converted to in this example? (heat) Add to LGO. Light can be absorbed and changed to heat. Extension: If available, play Bill Nye’s Classroom Edition DVD LIGHT AND COLOR. Go to Watch Program Section: Science Standards Clips, Clip 3 Light can be absorbed and changed to heat.

Electromagnetic Spectrum 1) visible light: humans can see. 2) Radio waves: carry signals to wireless devices like cell phones or computers. 3) Microwaves: when absorb the energy from the waves the food become hot. 4) Infrared: from the lamp keep the food warm. 5) X-ray: bones absorb more than muscles or skin so they appear lighter. 6) Ultraviolet: can harm your skin.