Chapter 10 , Lesson 4 "What is Light"

Materials:

• Worksheet, 10-04 "What is Light

Objective:

• Students will define light and explain how visible light is produced.
• Students will describe the nature of light.
• Students will describe the visible spectrum.

Anticipatory Set:* Most religious books begin with a discussion of light. After all with no light there would be no life. All life on planet earth originates with the energy from the sun. That light energy if first used by plants to turn carbon dioxide into sugars. From there some animals eat plants and others eat other animals Some even feed on dead plants and animals and still others will eat just about anything but it all starts with the light energy from the sun. But what is Light? That is what we are figuring out today.

Teacher Input:* Have the students set themselves up with a note sheet like this. As we cover each section of light have the students work to fill in the space under the heading. Show the students a picture of the three ways in which heat is transferred. Remind them that sound energy is like conduction or convection because it moves molecules when it hits them. Light is more like radiation it does not depend on other molecules to transfer the energy along. It travels as its own unit call a photon and moves until it hits something solid and then it expresses itself. It travels as an actual particle known as a photon. This photon hits our eye and then the eye can tell which wavelength of light it is for a certain range of waves. Just as the ear has a limited range that it can hear sounds. So every beam of light has millions of photons and they may be traveling at many different wavelengths. Next lets take a closer look at the wave.

Remember that sound waves travel outward in all directions. Light waves travel more in a straight line but still with a wavy pattern. Remember the idea of cycles. Light is just a small range of wave cycles. Photon particles travel at waves with closer and further apart cycles than just visible light. Explain this graph. Unlike sound, light travels through empty space and much faster than sound (300,000 KPS) we do not know of anything that moves faster than this. In fact light travels much faster through empty space than it does once it starts bouncing off of particles in our atmosphere and there are many things that light can't move through at all. Sound can move through many more things than light.

Lastly we are going to take a closer look at visible light. Recall that light is part of a larger energy system, the Electromagnetic waves. Our eyes can interpret photons traveling at the wavelengths from about 380 to almost 800 nanometer cycles. If we are seeing red the wavelengths of the photons are near 700 nanometers. If we are seeing blue or purple the wavelengths are near 400 nanometers. The light we see coming from the sun contains all the wavelengths of light but contains more of some than others. If we are seeing equal proportions of light across the entire range then we see white light. You have probably noticed these different colors before. All of you have seen a rainbow before. When light enters a raindrop the drop bends the light a little the shorter waves bend less than the longer waves so the colors get separated by the drop of water. We also have a man made tool to do this called a prism. Many of you probably played with this before. How can you easily remember the colors that make up the spectrum? All you have to do is think of a guy named Roy G Biv.(Red, Orange, Yellow, Green, Blue, Indigo, Violet) The last thing I want to discuss is how we see objects using light. When light shines on an objects some to the wavelengths of light get absorbed and some bounce off the object. Those colors that bounce off are the ones your eyes see. So if a leaf is green to your eyes that means it absorbed every color but green. Green was reflected off the leaf and picked up by your eye. What color is absorbed by this horse? (All of them)

Guided Practice:* Students will complete the questions on Page 293 as a group.

Independent Practice:* Students will complete the worksheet, 10-04 "What is Light" while they read the section in the book.

Check for Understanding:* After reading the section and completing the worksheet, students will take the quiz 10-04 "What is Light".

Duration:

30 minutes + 10-15 for Independent Practice (Could be longer if taken for homework).

Alaska Content Standards Addressed in this lesson:

• SCI A-1 Students will understand models describing the nature of molecules, atoms, and sub-atomic particles and the relation of the models to the structure and behavior of matter (Structure of Matter);
• SCI A-5 Students will understand the strength and effects of forces of nature, including gravity and electromagnetic radiation (Forces of Nature);
• SCI A-15 Students will use science to understand and describe the local environment (Local Knowledge); and: