Electromagnets

Core Idea

An electromagnet is a magnet made by wrapping wire around an iron nail or rod and running electricity through the wire. When the electricity flows, the nail becomes a magnet that can pick up paper clips and other iron objects. When the electricity stops, the magnetism goes away. Unlike permanent magnets, electromagnets can be turned on and off, and their strength can be changed by adding more wire coils or more battery power.

How It's Best Learned

Have students wrap insulated wire around a large iron nail, connect it to a battery, and count how many paper clips it can pick up. Change the number of coils and the number of batteries and compare results. Turn the battery off to see the magnetism disappear.

Common Misconceptions

• Electromagnets are permanent. (They only work when electricity is flowing; turn off the current and the magnetism stops.)
• Any wire carrying electricity is an electromagnet. (A straight wire produces a very weak magnetic field. Coiling the wire concentrates the field and makes a useful electromagnet.)
• Electromagnets are always weaker than permanent magnets. (Very powerful electromagnets can be far stronger than any permanent magnet.)
• The nail creates the magnetism. (The electricity in the wire creates the magnetic field; the iron nail strengthens it by becoming temporarily magnetized.)

Explainer

What if you could build a magnet that turns on and off with the flip of a switch? That is exactly what an electromagnet is. Take an iron nail, wrap wire around it many times, and connect the wire to a battery. The moment electricity flows, the nail becomes a magnet. Turn off the battery, and the magnetism disappears. This ability to control magnetism is what makes electromagnets so incredibly useful.

Here is how it works. When electric current flows through a wire, it creates a small magnetic field around the wire. A straight wire's field is too weak to notice. But when you coil the wire into a tight spiral around an iron core, each loop's magnetic field adds to the next. The iron core strengthens the field even more by aligning its atoms with the magnetic force. The result is a magnet strong enough to pick up handfuls of paper clips or, in industrial versions, entire cars.

You can control the strength of an electromagnet in two easy ways. First, add more coils of wire — each coil adds more magnetic force. Second, increase the electric current by using a stronger battery or more batteries. Scientists and engineers adjust these two factors to make electromagnets as strong or as weak as they need for any job.

Electromagnets are everywhere in modern life. Inside a junkyard crane, a giant electromagnet picks up scrap metal and drops it by cutting the power. Inside your doorbell, a small electromagnet pulls a metal arm to strike the bell. Electric motors — in fans, washing machines, and electric cars — use electromagnets to spin. MRI machines in hospitals use extremely powerful electromagnets to create images of the inside of your body. The combination of electricity and magnetism is one of the most powerful partnerships in all of science.