Electricity and Magnetism

Why does the compass respond when it is near an electrical wire with current flowing through it?

We can conclude from this experiment that an electric current causes a magnetic field around it just like a magnet causes a magnetic field. When you moved the compass near a bar magnet, the needle pointed toward the magnet's magnetic field and not toward the north. When you put the compass near the electrical wire with current flowing through it, the compass did not point north; instead, the compass needle pointed in the direction of the current's magnetic field.

Ferromagnetic Objects in Magnetic Fields

Now we have established that a conductive wire with a current flowing through it has a magnetic field. If we put a ferromagnetic object in this magnetic field, the object will concentrate the strength of the field and cause the object to become magnetic. Once the current flow in the line stops, the magnetic field disappears and the object stops acting like a magnet. However, the magnetic field of one wire is small and does not have much strength, so it can only make temporary magnets from small objects. But, let’s say that we take a wire and coil it several times to form a long coiled piece of electrical wire, and then we turn on the current. We would have a magnetic field much bigger and stronger than we would without the coiled piece of wire, and we could magnetize even larger objects.

An iron bar placed through the center of the coiled wire would become a temporary magnet, called an electromagnet, as long as the electric current is flowing through the wire.

Warning: Current may need to be restricted to prevent overheating the wire and to prevent damaging the battery.

You can also make an electromagnet by passing the electric current directly through the ferromagnetic object. Electromagnets are discussed in more detail in a following page.