Overview: One of the primary goals of this unit is to ensure that students know the fundamental differences between radio and sound waves. Through participation in this lesson, students will examine the characteristics of both types of waves.
Purpose: To identify and explore various characteristics of radio and sound waves.
- Examine their own prior knowledge and understanding of radio and sound waves.
- Discuss the characteristics of each type of wave.
- View and experiment demonstrated by the teacher to show the differences in the two waves.
Students can use this site to research and report on special topics related to sound including: ultrasound, infrasound,
echolocation, sonar, and breaking the sound barrier. They can also research the different types of waves included in the electromagnetic spectrum, which include: cosmic rays, gamma rays, x rays, ultraviolet rays, light rays, infrared rays, microwaves, and radio waves.
- Have students answer the following questions individually:
- How are sound waves produced?
How are radio waves produced?
- How do sound waves travel?
How do radio waves travel?
- How fast do sound waves travel?
How fast do radio waves travel?
- Have students work in pairs to compare answers and make any needed changes to their answers.
- Have students work in groups to compare answers and make any needed changes to their answers.
- Record each groupís answers on the board.
- Lead a class discussion, which will lead students to the correct answers and provide demonstrations to help develop student understanding.
- Sound waves are produced by objects, which vibrate rather rapidly. This can be demonstrated by feeling your throat while speaking, seeing a speaker vibrate as the sound comes out, or striking a tuning fork.†
Radio waves are produced by moving charged particles. An example of this is an electric current in a wire. This can be demonstrated with a wire, a 6-volt battery and a small radio. Turn the radio on AM so that static can be heard, attach one end of the wire to the battery. Touch the other end of the wire to the other battery terminal and have students record their observations. (When the other end of the wire is touched to the other battery terminal, you will hear the radio waves, which reach the radio get turned into sound waves, which your ears can hear.)††
- Sound waves travel through a medium. If there is no medium then there will be no sound. Show the included video of a bell in a vacuum. When all air is removed there is no medium for the sound waves to travel through so no sound is heard.†
Here is a video demonstrating this concept:
MPEG Video (10MB - 1 hour on 56k modem,
1-2 minutes on high speed connection)
Radio waves travel like light waves. They can be absorbed, reflected or transmitted. Using the same demo from above, wrap the radio in heavy-duty aluminum foil. Now touch the wire to the battery and have students record their observations. (When the wire is touched to the battery the radio waves cannot reach the radio because some of the energy is absorbed and some is reflected by the aluminum foil so very little is able to get through. These waves do not require a medium to travel through. A perfect example of this is satellites orbiting in outer space. They transmit radio waves through space to antennas here on the ground.)†††††††††††
- Sound travels at approximately 1,100 feet per second (766 miles per hour). Radio waves travel at the speed of light, which is approximately 186,000 miles per second. This means that in the time radio waves travel the length of a football field, light can travel further than all the way around the world. You can demonstrate this on the football field with a balloon and 2 walkie-talkies from Radio Shack. Have two students walk across the football field with the balloon and one walkie-talkie. Turn on the both walkie-talkies. The students with the balloon should then press and hold the talk button before popping the balloon. On the other end simply listen. Have students record their observations. (You should observe that the sound of the balloon was first heard over the radio and shortly afterwards through the air.)††
Have students answer the following questions:
- Which type of wave is produced by a vibrating object? (sound)
- Which type of wave can travel through outer space? (radio)
- Which type of wave travels at the fastest speed? (radio)
- Describe one situation when it would be better to communicate with a sound wave instead of a radio wave.
- Describe one situation when it would be better to communicate with a radio wave.
- Draw a picture of the last experiment. In your drawing include both people, their ears, their walkie-talkies, and the balloon. Show the paths of the sound waves using one color and of the radio waves using a different color. From your drawing, explain why you first heard the balloon pop on the walkie-talkie.