Grade Level: 6th – 8th grade
Subject Matter: Physical Science
National Standards: NS.5-8.1, NS.5-8.2
Reel of insulated copper wire - available in electronics or hardware stores
Three-inch nails – one per student or group of students
Double A (AA) batteries – one per student or group of students
Paperclips – several for each student
Small round ceramic magnets – one per student or group of students. These can be bought from Carolina.com. Here’s a link to the type of magnet you need:
Boom box radio - must have speaker wire output port
Roll of masking or Scotch tape
Scissors – one pair per student or group of students
Sound: vibrations transmitted through an elastic material or a solid, liquid, or gas.
Magnetic Field: the space surrounding a magnetized body or current-carrying circuit in which the resulting magnetic force can be detected.
Electromagnet: a type of magnet whose magnetic field is produced by the flow of electric current. The magnetic field disappears when the current ceases to flow.
Insulator: a material or device that prevents or reduces the passage of heat, electricity or sound.
1. Tell students that before they make a speaker, they have to know how an electromagnet works. Review the definition of an electromagnet. Can they think of a way to make a simple electromagnet?
2. Have students tightly coil the insulated copper wire around half of the nail until that portion of the nail is covered twice. Make sure students leave free at least 10 inches of wire on each end of the coil.
3. Use the scissors to strip about an inch of the insulation from each end of the free wire. Ask students why the wire needs to be exposed. Have students tape one end of the wire to one end of the battery.
4. Have students connect the other free end of the wire to the other end of the battery. Make sure students do not tape this end, since the coil will get hot if it is connected for too long.
5. Place a few paper clips in front of each student. Ask students to predict what will happen if the nail comes close to the paperclips. Have students pass the tip of the nail next to the paperclips. What happened?
6. Have students connect and disconnect the wire from the battery while touching the paper clips. What happens to the paper clips? Tell students that they have just made an electromagnet. Why are electromagnets useful?
Activity 2 – Make A Speaker
1. Tell students that now they will create a speaker, using the same basic principles that they learned from making an electromagnet.
2. Hand out to each student a plastic cup, a round ceramic magnet, tape and insulated copper wire. Ask students to draw a diagram, to show how they would make a speaker using these materials. Compare and contrast the various diagrams and have students explain their design.
3. To begin building the speaker, have students tape the round ceramic magnet inside the bottom of a plastic cup.
4. Coil the insulated copper wire 25 times into 1½-inch diameter circles with 10 inches of wire hanging free from each end. If needed, students may use an appropriately-sized round object to wind the coil, and then slide it off when they’re done.
5. Tape the coil to the bottom of the cup and make sure to strip a few inches of insulation from the end of each wire.
6. Have students test their speaker by connecting the two free ends of the coil to the “speaker out” of the radio. Students can hold the cup or let it rest on the table. Ask students to predict what will happen if the radio is turned on.
7. Turn the radio on and have students observe and describe what happens. What happens when you increase the volume?
8. Allow students to rebuild their speaker according to their own diagrams, if they differ from the steps above. Discuss the results. Why did or didn’t their diagram work?
An electromagnet is a magnetic field that can be turned on or off. A simple electromagnet can be made by coiling wire around a nail and connecting the ends of the coil to a battery. The battery produces an electric current that flows from the battery through the wire. As the current flows through the wire, it creates a magnetic field. Once the current ceases to flow, the magnetic field disappears. Electromagnets are useful for devices that need magnets that can be controlled. A speaker uses electromagnets to produce sounds or vibrations.
• What is needed to make the speaker louder?
• How could you improve the sound quality of the cup speaker?
• What would happen if you replaced the nail in the electromagnet activity with aluminum foil? Or with a plastic core, like a pen?
Experiment with different numbers of turns on the electromagnet from the first activity. What is the magnetic power of a single coil wrapped around a nail? Or 10 turns of the wire? 100 turns? How about changing the thickness of the nail? Have students measure and compare the electromagnet’s "strength" by how many paper clips it can pick up.