Students know electric currents produce magnetic fields and know how to build a simple electromagnet.

This standard introduces the intimate connections between electricity and magnetism. As discussed in the CONCEPT OVERVIEW, electricity and magnetism are part of the same force, the electromagnetic force. In our everyday world, we tend to experience only specific, limited manifestations of this much more general force. Electricity and magnetism are much more than metallic objects sticking to refrigerators or electric currents flowing in wires.

People generally have two kinds of experiences that illustrate the intimate relationship between magnetism and electricity. The simplest experience is the construction of an electromagnet. Somehow electricity flowing in a coil around a nail will make the nail act like a magnet. This electromagnet will pick up paper clips, and it will repel and attract the two poles of a permanent magnet. If the electricity stops flowing, the nail stops acting like a magnet. If we reverse the flow of electricity through the coil, then the poles of the nail electromagnet change orientation.

The second experience involves noting the effect of electric current on a compass needle. If a compass is placed directly under a wire that is connected to a battery, then the flow of electricity can be seen to affect the compass needle. Reversing the direction of electricity flow causes a change in the direction of the deflection of the compass needle. The simplest explanation of this effect is that the flowing current produces a magnetic field that affects the orientation of the compass needle.

A third example is harder to demonstrate but is the basis of most of the electricity that we use in our homes. The previous two examples show that a moving electric current generates a magnetic field. In this third example, it is the magnet that moves, and the result is that it produces an electric current. Moving a bar magnet in and out of a hollow, cylindrical wire coil can cause electricity to flow within the coil. This is actually the underlying basis of generators that make electricity by moving huge magnets in and out of an apparatus with many coiled wires. The moving magnets cause electricity to flow in the wires, and this electricity is distributed to homes and industry.