Lesson 3: Light

Day 3

Activity 7: Reflection and Absorption

Materials: dark cloth (kit), flashlights (kit), mirror (kit), piece of cardboard (kit), piece of white paper (kit), piece of wood (kit), tape, white paper
Note: Be sure to keep the mirror from this activity to use in the Living Seas unit.

Things that make light are called light sources. Things that are not light sources give off light by absorbing some light colors and reflecting others. A blue object appears blue because it absorbs all colors except blue. A yellow object absorbs blue light but reflects red and green light (red and green light make yellow). What color do you think you will see if an object absorbs all the colors of the rainbow (all the colors of light) and reflects none of them?

Reflection occurs when light bounces off of objects. The amount of light reflected off of an object depends on whether the surface is rough or smooth. On a rough surface the light scatters, but if a surface is smooth and flat, the light will bounce off it at equal angles. The angle at which light hits a surface is called the angle of incidence. The angle at which light is reflected is called the angle of reflection.
Angles of Incidence and Reflection
Watch the video to find out more about absorption and angles of incidence and reflection. (The video covers refraction as well, which you will experiment with in Activity 8.)
Web Link
Gather the materials listed on the "Reflection and Absorption" activity page. Perform the following two tests.

Test 1:

  1. Find a room that can be darkened (by closing curtains or turning off a light). Place the cardboard, fabric, wood, and paper in a row on the floor or on a flat surface.
  2. Darken the room.
  3. Shine a flashlight onto each material, one at a time. Make sure you and the flashlight are about the same distance from each of them.
  4. Notice what color you see for each object, and record your results on the "Reflection and Absorption" activity page.
  5. Decide whether the objects are reflecting light, absorbing light, or both. If something absorbs all the colors of the rainbow and reflects none, you will see black. If something reflects all of the colors and absorbs none, you will see white. If you see a color other than black, you know your item absorbs some colors and reflects others. Record your results on the activity page.

Test 2:

  1. Find a room that can be darkened (by closing curtains or turning off a light). Line up the mirror, cardboard, fabric, wood, and paper in a row on the floor. Space the objects about 6 inches apart from each other, and 6-12 inches from an empty wall, as shown in the following illustration.
  1. Tape white paper to the wall behind each object, a few inches above the floor.
  2. Darken the room.
  3. Shine the flashlight at an angle on the mirror.
  4. On the "Reflection and Absorption" activity page, draw the angle of incidence you observe for light coming from the flashlight toward the mirror and the angle(s) of the light going away from the mirror toward the wall (the angle of reflection). The following illustration is an example of how you might draw the mirror's angles of light on the activity page. You can also refer to the diagram at the beginning of this activity.
  1. As you draw, notice how bright or dim the light on the wall is, and how spread out the light is. Use arrows of different sizes and weight to communicate these details as well as to capture the angles of the beams of light. For example, the mirror will have a bright, focused beam, so you may show that by drawing a single arrow that is thick and dark.
  2. Keep the angle of the flashlight the same and repeat for the other four objects. Unlike with the mirror, it will be hard to see exactly where the light is reflecting onto the wall. To get an idea of where the light is reflecting, you might want to change the angle of the flashlight and watch what happens to the light on the wall. Return to the original angle before drawing your pictures. In your drawings, remember to show these three things: how bright or dim the light on the wall is, how spread out the light on the wall is, and the angles of the beams of light.
  3. Answer the question at the bottom of the activity page and discuss your findings with a parent.
Note: Be sure to keep the mirror from this activity to use in the Living Seas unit.

In this activity, your child will test light reflection and absorption. It must be performed in a room that can be darkened.

If space is an issue, Test 2 can be performed with only one sheet of paper taped to the wall. Your child will need to switch out the sample each time. It is easier to compare the samples with separate pieces of paper taped to the wall, but either method will work.

Discuss which surfaces reflected more light and which absorbed more light. Discuss whether some objects absorbed some light and reflected other colors of light. Analyze the angles your child observed, and discuss whether some of the light on the wall may have been reflected from the surface the objects were sitting on.

For Test 1, your child should note that the white paper reflected all light and the dark/black fabric absorbed all light. Because they look brown (and not white or black), the cardboard and wood both absorbed and reflected light.

For Test 2, results and drawings will vary. See the following example of a diagram for the piece of dark fabric (as well as the sample diagram for the mirror in the activity instructions). Your child should have noticed that the angle that the light travelled from the object to the wall changed depending on the angle from the flashlight to the object. The smoother the surface of the object, the more the light was all reflected at the same angle. The light hitting the wall from the mirror was much more highly focused than the light reflecting from the paper, cardboard, fabric, and wood.

The wood and dark fabric may seem to reflect very little light toward the wall because their irregular surfaces scatter the light in many directions rather than staying focused in a beam. Your child may also notice that the darker colored objects reflected less light because they absorbed more light. In general, your child should notice that the amount of light reflected onto the wall, from most to least, will be similar to this: mirror, white paper, wood and cardboard, fabric.

Activity 8: Refraction

Materials: clear glass cup, flashlights (kit), pencil, white paper
Refraction is the bending of light. Light bends as it passes from one transparent medium to another at an angle. Light responds differently to transparent objects, such as glass or water, than it does when it hits objects that you cannot see through.

Put a pencil in a clear glass of water. What does the pencil look like? The light is traveling at an angle, so one part of the light hits the water before the other. The water bends the light. You can also observe refraction by going in a dark room, putting the glass of water on a white sheet of paper, and shining a flashlight through the water. What happens? Does the light that hits the glass of water come out in the same way it went in?

A magnifying glass makes things look larger. Have you ever wondered why? The lens refracts light. The lens is wider in the middle than around the edge, and the bottom curves outward. This makes the object appear larger. If the bottom curved inward, the refracted light would make the object look smaller. Telescopes, microscopes, and cameras all refract light.
Discuss the difference between reflection and refraction. Refraction occurs when light passes through a transparent surface and the light is bent. Transparent surfaces do not reflect or absorb light, they bend light.

Activity 9: Shadows

Materials: a variety of objects, flashlights (kit)
What happens when you go in a dark room, shine a flashlight on the wall, and put your hand between the light and the wall? Try it now.

A shadow is cast when you block out light. Practice making different types of shadows in a dark room with a flashlight and a variety of objects. It might be helpful to have an assistant hold the light source. How do you make the shadow change? On the "Shadows" activity page, write three observations about shadows.

Watch the following video about shadows. When you are finished, complete the rest of the "Shadows" activity page.
Web Link
Student Activity Page
For this activity your child will experiment with making shadows. Discuss your child's observations about how to change a shadow. Observations may include that you can change a shadow by moving the light source from side to side, moving the light source closer or further away from the object, or moving the object closer or further away from the surface that the shadow appears on.

Check that your child correctly identified translucent, transparent, and opaque objects. Help him as needed if he has trouble creating an umbra and penumbra.