23.1 Electric Current and Magnetism In 1819, Hans Christian Oersted, a Danish physicist and chemist, and a professor, placed a compass needle near a wire through which he could make electric current flow. When the switch was closed, the compass needle moved just as if the wire were a magnet.

An apparatus can be built that shows the magnetic field around a straight wire. The compass needles all form a circle when the current is switched on in the wire.

23.1 Electric Current and Magnetism Two wires carrying electric current exert force on each other, just like two magnets. The forces can be attractive or repulsive depending on the direction of current in both wires.

The direction of the force can be deduced from the right-hand rule. If you bend the fingers of your right hand as shown, your thumb, index, and middle finger indicate the directions of the force, current and magnetic field.

23.1 Electric Current and Magnetism The magnetic field around a single wire is too small to be of much use. There are two techniques to make strong magnetic fields from current flowing in wires: Many wires are bundled together, allowing the same current to create many times the magnetic field of a single wire. Bundled wires are made into coils which concentrate the magnetic field in their center.

When wires are bundled, the total magnetic field is the sum of the fields created by the current in each individual wire. By wrapping the same wire around into a coil, current can be “reused” as many times as there are turns in the coil

Coils are used in electromagnets, speakers, electric motors, electric guitars, and almost every kind of electric appliance that has moving parts.

23.1 The true nature of magnetism The magnetic field of a coil is identical to the field of a disk-shaped permanent magnet.

23.1 Magnetic force on a moving charge A magnetic field that has a strength of 1 tesla (1 T) creates a force of 1 newton (1 N) on a charge of 1 coulomb (1 C) moving at 1 meter per second. This relationship is how the unit of magnetic field is defined.