What Happens to a Current-Carrying Wire in a Magnetic Field?

The Idea

The heart and soul of an electrical motor is movement created when magnets repel each other. The discovery by Michael Faraday that a force is produced when current flows through a magnetic field was a groundbreaking discovery, which paved the way for the eventual development of the electric motor.

What You Need

• powerful horseshoe magnet
• DC voltage source, such as an adjustable power supply, a motorcycle battery, or a car battery
• about 1 meter (a few feet) of insulated wire
• ring stand with clamps to position the wire

Method

1. Set the horseshoe magnet on the table.
2. Position the wire midway between the north and south poles of the magnet. The wire should run perpendicular to the two ends of the magnet and it should be able to move.
3. Attach one end of the wire to the negative terminal of the power supply, as shown in Figure 112-1.
4. Briefly touch the other end of the wire to the positive terminal and observe the wire passing between the poles of the magnet. If you are using an adjustable power supply, start with a lower-current output setting and slowly increase it until the wire responds. Because there is no resistance besides the little resistance the wire offers, a high current may flow that may cause a fuse or circuit breaker to blow.

Expected Results

With current flowing in the wire, the magnet pushes the wire away from the magnet.

Why It Works

A force is exerted on a moving charge (or current) in a wire moving perpendicular to a magnetic field.

Other Things to Try

Repeat this with a tight coil of the wire in the magnetic field. Compare with the response of an uncoiled wire.

The Point

A magnetic field exerts a force on a current-carrying wire. The direction of that force depends on the direction of current flow and the orientation of the magnetic field according to the right-hand rule.

This article is brought to you by:

From this Book:

125 Physics Projects for the Evil Genius
Buy this book »