Webs Wires and Waves: The Science & Technology of Communication


Listen Up!: Speaker-in-a-Jiffy

Activity 3 Overview
Youngsters will create their own paper cup speaker and hook it up to a small radio.

Estimated Time and Age Level
Advance Preparation: 20 minutes
Activity: One 50-minute session
(Ages 11-14)

Materials
(Per Team)
1 paper cup (4 oz. to 10 oz.)

1 small bar magnet (approx. 1 or 2 cm. wide and at least 3 cm. long; a bar-shaped stack of tiny magnets will also work)

masking tape

2 ice cream sticks

3-by-5-inch index card

scissors

wire stripper (if available)

6 meters (20 feet) of thin enameled wire

emery paper, 220 grit or finer (optional)

(For the whole group)
At least 1 small transistor radio with AM reception

At least 1 monaural transistor radio ear plug (generally available from Radio Shack® or other electronics supply stores for about $2)

Preparation
Cut about 3 meters (10 feet) of thin enameled wire for each group. Using the scissors or the wire stripper (if one is available), scrape about 1 centimeter of coating off of the tips of each length of wire. If you want, ask youngsters to help by using emery paper to clean the ends of the wire (as well as assisting with the other Preparation steps).

To enable youngsters to hook up their speakers to the radio, you'll need to prepare a simple wire "jack" or connector using the monaural ear plug. Use scissors to cut the cord at the end near the ear plug. Discard the ear plug. Using the scissors or wire stripper, if you have one, carefully strip away two centimeters of plastic coating from the cut end. (Note: if an ear plug of this sort is not available, you can substitute an inexpensive pair of personal stereo headphones. You'll have to separate the wires and pull back the loose strands of copper wire you'll find beneath the outer plastic coating. You won't be needing them. Then carefully strip two centimeters of coating off of the remaining wire and your "jack" is complete.) Make one jack for each radio. The more radios you can collect, the less waiting each team will have to do.

Set up at least one radio to use for this activity. The best kind would be a small transistor radio that has a speaker and a headphone jack. You could substitute a personal radio that uses only headphones, but since such radios use very little power, youngsters will need to make their speakers very well to get them to work. Do not use an expensive stereo system. Large amplifiers can be damaged by paper cup speakers. However, any radio that has a compartment for batteries will work fine.

Print out 1 copy of the Speaker-in-a-Jiffy directions for each team.

Set out the materials in a central location.

Procedure
Set the stage for the activity by asking youngsters to reprise lessons learned from the String It Along activity. Discuss how real telephones have small speakers inside them that change electricity into the sound vibrations that we all hear when talking with our friends. To discover exactly how these speakers work, youngsters are now going to make their own "Speaker-in-a-Jiffy"

Hand out the prints of the Step-by-Step box. If necessary, help youngsters assemble their speakers. Younger children might have trouble making neat coils, and that is critically important. To help them with this step, suggest that they keep wrapping the wire about ten times around the tube, and then pushing the coil down to one end. They'll find it easier to keep the coil neat if they keep pressure on the wire the entire time they're wrapping it.

After youngsters complete their speakers and (taking turns) hook them up to the radio, they should be able to clearly--if somewhat faintly--hear radio signals coming through their speakers. If they don't, have them make sure the magnet is attached to the bottom of the cup and can move freely within the coil. They can also try pushing the ice cream sticks apart to immobilize the coil.

Challenge youngsters to relate what they've just seen (and heard) with what they discovered about sound vibrations in Activities 1 and 2. What is vibrating in the cup that produces sound? What's making it vibrate? They may be able to guess that the magnet is vibrating because it has been stimulated in some way by the radio. (In short: the radio's electric current is generating its own magnetic field, which repels and attracts the magnet--i.e., makes it vibrate. The magnet taps the bottom of the cup and makes it vibrate as well, pushing the air on the other side in and out in the same pattern as the one the original sound wave produced at the radio station. See Unit 4 for more information.)

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