To learn how to construct and use an electromagnet. To learn that electromagnets are temporary magnets and work only when electricity passes through the coil of wire.
People use the power of magnets in many ways. Magnetism and electricity are closely related. In an electric generator, an electric current is set up in a coil of wire that moves through a magnetic field. An electric current moving through a wire coil wrapped around an iron core produces magnetism. The close interrelationship between magnetism and electricity has many applications.
By exploring magnets, students are indirectly introduced to the idea that there are forces that occur on earth which cannot be seen. This idea can then be developed into an understanding that objects, such as the earth or electrically charged objects, can pull on other objects. It is important that students get a sense of electric and magnetic force fields (as well as of gravity) and of some simple relations between magnetic and electric currents. (Benchmarks for Science Literacy, p. 93.) This lesson continues the exploration of magnetism begun in Science NetLinks lessons Magnets 1: Magnetic Pickups, Magnets 2: How Strong is Your Magnet?, and Exploring Magnetic Fields. Before doing this activity, students should have built simple electric circuits with batteries and flashlight bulbs.
In this lesson, students will make a simple electromagnet by wrapping a wire around a nail and attaching the ends of the wire to a battery to make an electric circuit. As current flows through the coil, a magnetic field is produced and the nail is magnetized. Lessons such as this help to build a foundation upon which students can develop their ideas about gravitational force and how electric currents and magnets can exert a force as well.
Begin with a brief discussion in which students can review concepts about magnetism, using questions such as these:
- What is a magnet?
- What is a magnetic field?
- Can you make a magnet?
If students' responses indicate that they need to review magnetism, you can refer them to How Electromagnets Work for a brief refresher.
Then say to students, “Electromagnets are temporary magnets that let us turn magnetic fields on and off so we can control the magnetic energy.” Then ask students to speculate on why it is advantageous to turn the fields on and off. Tell students that they will conduct an activity to explore how electromagnetic fields work.
Pass out the Build an Electromagnet student sheet and have students do the activity in pairs. Students will build an electromagnet and test its strength. To save time, you can pre-strip the ends of the wire for each pair of students. You can use a wire stripper, scissors, or a sharp knife to remove the insulation.
Before students begin to work on their own, make sure that each group has the needed materials to build their electromagnet. To help students, you can ask questions such as the following before they begin:
- Do you think an electromagnet will be attracted to the same things as a regular magnet?
- Will it be attracted to all metal things?
- Will it be attracted to other magnets?
As students are building the electromagnet, walk around the class to make sure that they are on track. Ask questions such as:
- What happens to the electromagnet if you disconnect one of the wires from the battery?
- How many turns of the wire does it take to pick up a paper clip?
- Are more turns better?
After students have built their electromagnet and tested it, you could ask questions such as the following to extend their ideas:
- What happens if you build another electromagnet using a different size battery?
- How many paper clips will this new electromagnet pick up?
- Does using a different size battery (“A” versus “C”) make a difference?
- What things are attracted to a permanent magnet, such as a refrigerator magnet? Are these the same things that are attracted to the electromagnet?
- Are there any differences between what the permanent magnet and the electromagnet can do?
After students have completed the activity, discuss the questions on their student sheets:
- What is traveling through the wires? Where does the electricity come from?
- Is an electromagnet a temporary magnet or a permanent magnet? Why is it a temporary magnet?
- How can you measure the strength of your electromagnet? How can you make your electromagnet stronger?
Do not dismantle the electromagnets until you are finished with electromagnet activities, but be sure they are disconnected from the batteries at the end of your class.
When you are finished with electromagnet activities, unwrap the wires and be sure the electromagnets are not connected to the batteries. Students can label their electromagnets with tape and use them over and over.
Next, using the Electromagnets student esheet, students will explore Using Electromagnets. After students have explored the site, review how electromagnets are used in each of these items:
- electric bell
- electric motor
To assess student understanding, instruct your students to write several paragraphs to summarize some of the uses of electromagnets described in the Web resource. They should explain the function of the electromagnet in the devices described. They also should discuss how the electromagnets in those devices are like the ones they built.
After doing the activity and exploring the website, students should understand that when an electric current flows through a wire, a magnetic field is produced around it. This concentrates the magnetic field, especially if we put an iron bar in the center of the field. They also should generally understand that there are two ways to increase the strength of an electromagnet. One is by adding more length to the wire (more coils). The other is by increasing the amount of electricity going through the wire. By increasing these two things, engineers have developed very powerful electromagnets such as the enormous ones used in junkyards to lift large piles of metal.
More detailed information about magnets and electromagnets can be found at Magnetic Fields.
More activities to try with electromagnets can be found at How Electromagnets Work: Experiments to Try.