# Electric Current Model

Science Snack
Electric Current Model
Use magnets to model the motion of electrons.
Electric Current Model
Use magnets to model the motion of electrons.

Model the motion of electrons through a wire by pushing on a circle of small magnets around the rim of a large magnet.

Tools and Materials
• Cylindrical magnet 1 inch (2.5cm) or larger in diameter
• Six small cylindrical magnets, about 0.25 inches (0.5 cm) in diameter and the same height as the larger magnet
• Optional: steel washer smaller in diameter than the large magnet
Assembly

Place the small magnets around the rim of the larger magnet. Use 4, 5, or 6 magnets depending on their size. There should be a small gap between them.

Note: Make sure the magnets are all clean and clear of iron filings or other dirt that might stop the magnets from rolling smoothly.

To Do and Notice

Notice how the small magnets repel each other and become equally spaced around the rim of the large magnet.

Use your finger to push one of the small magnets a short distance around the rim (see photo below). Notice that all the magnets around the rim move at the same time as the one you’re pushing. Each time a new small magnet arrives at the position vacated by the previous magnet, use your finger to push it along. Repeat until the original magnet returns to where it started.

If you have a steel washer that’s smaller in diameter than the large magnet, place the assembled magnets on a smooth surface with the washer under the larger magnet. The washer will keep the small magnets from rubbing on the surface as they move.

What's Going On?

If the central, large magnet has its north pole up, then, in order to stick to its rim, the smaller magnets must all have their south poles up. In this orientation, the smaller magnets all repel each other. This causes them to separate from each other by an equal amount.

When you push on one magnet it magnetically repels the magnet you push it toward. The magnetic repulsion travels at the speed of light, and the magnet immediately begins to move. It then pushes its neighbor so that, in a very short time, all the magnets are in motion. However, even though they all start to move immediately, their actual speed is determined by how fast you push the magnet under your finger. That motion is much slower than the speed of light!

This Snack models the current of electrons flowing in a wire: The small magnets represent the electrons, and your finger represents a battery. The magnets repel each other due to their orientation, while the electrons repel each other because they all have a negative electric charge.

Going Further

The magnets in this Snack model what happens in DC electrical circuits, such as the one that powers your car headlights. When you close the headlight switch, electrons move through your car’s wiring and the lights come on. The electrical force that makes the electrons move travels through the wire at a large fraction of the speed of light. As soon as the electrons in the headlights begin moving, the headlights come on, even though it takes a few hours for any one particular electron to travel through your car wiring from the battery to the headlights. Thank goodness there’s no need to wait for that electron to make the whole journey before you can see what’s in front of you when you’re driving!