Experiment 11.4: Making an Electromagnet

Explore magnetism by creating a magnetic field with electricity.

Student Information

Background Information

We have spent a lot of time discussing electrical charge and electricity. What about magnetism? Well, as James Clerk Maxwell demonstrated, and you learned in the last module about light, the force that is involved in magnetism is really the same as the force involved in electricity. Thus, a study of one is, in fact, a study of the other.

Nevertheless, you need to understand a few basics about magnets before you finish this module. Remember what you learned about electromagnetic waves in the last module: all magnetic force results from the movement of charged particles! Complete this experiment to help you see this.

Purpose

To explore magnetism by creating a magnetic field with electricity.

Materials

Safety Precautions

⚠️ IMPORTANT SAFETY WARNINGS

  • Always wear eye protection when conducting this experiment.
  • Only use the specified 1.5V battery. Higher voltages can be dangerous.
  • The wire will get hot during this experiment. Wear gloves if available.
  • Do not leave the wire connected to the battery for extended periods.

Procedure

Step 1

Lay the paper clip out on a table or desk.

Step 2

Touch the nail to the paper clip and then pull it away. Did the paper clip stick to the nail? Record your observations.

Step 3

If the insulated wire is not stripped so that bare conducting wire is exposed at each end, strip the wire like you did in Experiment 2.3.

Step 4

Wrap the wire around the nail as many times as you can. The tighter you can wrap the wire around the nail, and the more turns of wire you have, the better. In the end, your nail should look something like the one in Figure 11.28.

Figure 11.28 - Wire wrapped around nail

Figure 11.28

Step 5

Use the tape to attach the bare conductor on one end of the wire to one terminal of the battery, and then the other bare conductor to the other end of the battery. That way, electricity will flow through the wire. The wire will get hot, so wear gloves if the heat gets too uncomfortable.

Step 6

With electricity still flowing, touch the nail to the paper clip. What happens this time? Record your observations.

Step 7

Disconnect the wires from the battery and put everything away.

Data Collection

Initial Observation

What happened when you touched the nail to the paper clip before connecting the battery?

Electromagnet Observation

What happened when you touched the nail to the paper clip with electricity flowing through the wire?

Conclusion

Write a paragraph describing what happened. Explain how a magnet was created, making connections to the text.

Understanding Magnetism

How Electromagnets Work

In the experiment, you wound a wire around a nail and then ran electricity through it, creating a magnet. The experiment demonstrated that the movement of charged particles (electrons, in this case) can create a magnetic force.

Well, that should make sense because we know that electricity is moving electrons. But what about solid things as permanent magnets? These magnets have no electricity hooked up to them, but nevertheless, they are magnetic. How is their magnetic force generated by the movement of charged particles?

Magnetic Materials

Remember that all matter is composed of charged particles because all atoms contain positively charged protons and negatively charged electrons. And also remember that the electrons in an atom are in constant motion. Thus, there is a continuous movement of electrons in all matter.

Why isn't all matter magnetic, then? Well, the movement of the electrons around the nucleus is only part of how this happens. Electrons also have a property which scientists call "spin." Spin refers to how the electron moves around its axis—think of a spinning top. Some electrons spin clockwise while others spin counterclockwise. It is this spin property that causes electrons to act like tiny magnets and produce tiny magnetic fields.

Magnetic Domains

In many materials, each electron is paired with another electron that spins in the opposite direction. These paired, opposite spinning electrons end up with their magnetic fields canceling each other out. As a result, these materials have extremely weak magnetic fields.

Other materials, however, have one or more unpaired electrons producing magnetic fields that are not canceled out. That's still not enough to produce a magnet, though. You see the magnetic fields of these electrons usually don't combine unless the arrangement of the atoms is just right. These materials will have weak magnetic fields.

In materials, like the iron nail you used in the experiment, the unpaired electrons make a strong magnetic field. Then the fields of these electrons combine to form what is called a magnetic domain. A magnetic domain is a cluster of many atoms that have their magnetic fields aligned and so act as a magnet. Materials, such as iron, can be magnetized (when exposed to electricity or another strong magnet) because they contain magnetic domains.

Figure 11.29 - Magnetic Domains

Figure 11.29: Magnetic Domains

Clusters of atoms in ferromagnetic materials form domains. If the domains are randomly oriented (top) the domains cancel each other out and there is no net magnetic field. If, under the influence of electricity or a strong magnet the domains align (bottom) the material emits a strong magnetic field. These domains may stay aligned for a long time.

It turns out that not all of the domains in a ferromagnetic material need to line up in order to make a magnet. In fact, only a small fraction of the atoms in a material need to line up to get some magnetic effect. As more domains line up, you have more electrons simulating the flow of electricity, and the result is a stronger magnet. Thus, the strength of a magnet depends on what percentage of the domains in the material are aligned. The larger the percentage, the stronger the pole of a magnet.

Magnets and Magnetic Forces

If you've played with magnets at all, you'll recognize that there are two "sides" to a magnet. In physics, we call them the north pole and south pole of a magnet. In many ways, the poles in a magnet are much like charges. For example, if you point the north pole of a magnet toward the south pole of another magnet, the two poles will attract each other. If, however, you point the north pole of a magnet to the north pole of another one, they will repel each other. Thus, as I'm sure you're already aware, opposite poles attract one another, and like poles repel one another, just like charges.

The magnetic force, then, is the force a magnet exerts on another magnet, on metals, or on moving charges.

Figure 11.31 - Magnets

Figure 11.31: Magnets

You can feel when magnets attract or repel other magnets. That is the magnetic force.

Magnetic Field Lines

All magnets are surrounded by a magnetic field that can exert magnetic forces. We can use iron filings (a ferromagnetic material) to visualize magnetic fields. Magnetic fields are strongest near the poles and will attract or repel another magnet or metal that enters the field.

Look at the drawing in Figure 11.34 (right). The arrows on the field lines show you where the north pole of a freely moving magnet will point if placed into the field. Notice that the arrows point away from the north pole of the bar magnet and into the south pole. Where the lines are closer together (at the poles), the field is stronger. Where the lines are more spread out (the middle of the bar), the field is weaker.

Figure 11.34 - Magnetic Field Lines

Figure 11.34: Magnetic Field Lines

Iron filings reveal the magnetic field lines of the magnetic field that surrounds every magnet (left). Field lines start near the north pole and extend toward the south pole.

Real-World Applications

We use magnetic fields for many things. For example, the tags that retail stores use to prevent theft use magnets. Have you bought a CD or DVD that had a tag like that shown in the top image of Figure 11.36? If you have, then you know you must walk through a pair of metal pedestals at the door of the store. These pedestals produce a changing electromagnetic field between them and have a receiver to pick up signals. If the cashier does not deactivate the tag on your purchase, the tag will set off the alarm.

The medical field makes use of magnetic fields in MRI (magnetic resonance imaging) machines. MRI uses the fact that body tissues contain varying concentrations of hydrogen atoms. Using magnetic fields and radio waves, MRI machines use changes in the spin of the nuclei of hydrogen atoms to create detailed "maps" of different body tissue. MRI can detect some kinds of cancer earlier than X-rays, and MRI is safer to use (long-term) than X-rays. MRI can also map images of areas, such as the brain, that X-rays cannot. MRI is a truly remarkable technology.

If you've ever used a compass, then you know Earth is like a giant magnet. A compass points north because it aligns with Earth's magnetic field.

Analysis Questions

1. What is the relationship between electricity and magnetism demonstrated in this experiment?

2. Why did the nail become magnetic when electricity flowed through the wire?

3. How would wrapping more turns of wire around the nail affect the strength of the electromagnet?

4. What would happen if you reversed the connections to the battery? Would the electromagnet still work?

5. What are magnetic domains and how do they relate to this experiment?

6. Why can't you split a magnet to get a single north or south pole (a magnetic monopole)?

7. Name three real-world applications of electromagnets.

Extension Activities