Electromagnets are different than the permanent magnets used in the other Try This at Home activities. They’re not magnetized metal: they’re basically a wire conducting electric current, which in turn generates a magnetic field. Magnetism and electricity are very closely related phenomena.
Electromagnets have a wide range of uses, from the MRI machines used in hospitals to remote-control toy cars to many appliances in your home. They vary in strength from very weak but sensitive electromagnets used to detect other magnets or electric currents to the huge research instruments used here at the Magnet Lab.
What you'll need
- One D-cell battery
- Insulated copper wire
- Iron nail or iron rod
- Paper clips
What you'll do
- Before you begin to build your electromagnet, let's check to see if the nails are magnets. Do they attract the paper clips?
- Connect the insulated wire to the battery. Make sure you complete the circuit by attaching the ends of the wire to opposite ends of battery. Place the compass under the wire. Is there any reaction?
- Disconnect one end of the wire. Wrap it around a nail 15 times before connecting it back to the battery. What do you see when you bring the compass near? Is this reaction different from what you saw when you placed the compass under the straight wire? Can you pick up paper clips with the wire? Can you pick up paper clips with the nail?
- Remove the nail from the wire without unwinding it. Will the wire pick up any paper clips? Will the nail alone pick up any paper clips?
- Place your compass under the wound wire. Do you get the same reaction as you did when you observed the compass in Step 4? How can you explain this?
What happened, and why!
In step 1, when you tested the nail to see if it was a magnet, you realized it was not because it did not attract the metal in the paper clip. However, iron nails can be magnetized. Your compass did not react to the wire because the wire by itself emitted no magnetic field.
In step 2, when you placed the compass under the wire, the needle deflected because the wire was now carrying an electric current generated by the battery, and current-carrying wires have a magnetic field around them.
In step 3, after you added the nail and coiled the wire around it, the compass picked up a much stronger magnetic field. That’s because a coiled wire creates a stronger magnetic field than a simple length of wire (the more coils, the stronger the field), and adding an iron nail in the middle boosts that field even more. The wire itself did not pick up the paper clip (its magnetic field was too weak), but the nail and coiled wire did.
In step 4, the nail picked up the paper clip this time because you had magnetized it by exposing it to the magnetic field of the current running in the wire. But without the nail inside it, the wound wire still didn’t produce enough of a magnetic field to pick up the paper clips.
In step 5, the compass measured a magnetic field in the wound wire (minus the nail) that was stronger than the field in the uncoiled wire, but weaker than the field in the coiled wire with the nail inside.
Did you know?
- The magnetic field of a refrigerator magnet is more than 10 times stronger than the Earth’s magnetic field.
- There are two units of measure for magnetic fields: gauss and tesla. One tesla equals 10,000 gauss. The Earth’s magnetic pull is about .5 gauss. A 1 tesla magnet is strong enough to pick up a car. Our strongest magnet at the MagLab is a whopping 45 tesla – the strongest sustained magnetic field on the planet.
Which of the following household items does not use an electromagnet?
- An automobile
- A washing machine
- A computer
- A stereo system
Answer - None of the above! OK, so we tricked you. The fact is, it’s hard to find an appliance that doesn’t have a magnet in it. Besides their obvious uses in can openers, magnets are a critical ingredient in the electric motors that make most appliances tick. Check out the below link to see how electric motors work.