… and how to make a compass using material that is found in most homes.

Human knowledge of magnetism began with magnetic stones. Prehistoric people observed that certain stones were attracted to each other and that iron was attracted to them. They discovered that if one of these stones is suspended so that it can turn freely, it always turns to a certain position. By noting the position of the stone the stone could be used to determine which direction is north without observing the North Star. In English such a stone came to be called a lodestone. In ancient Greece, a particularly good type of lodestone was called magnetite because it was found in an area of Greece called Magnesia. The word magnet came from magnetite. We now know that magnetite is an iron ore that has become naturally magnetized.

Ancient people made compasses in several ways including magnetizing iron needles. There are also several ways to make a compass at home. A compass requires something fairly light that is either a very small magnet or something light that can be magnetized using a permanent magnet. Most homes have refrigerator magnets, cupboards with magnetic latches or a screwdriver that has a magnet in it. A cupboard-door magnet can be used without removing it from the door.

In addition to a magnet, this project also requires a twist-tie like the ones used to close a bread bag, a straight sewing pin and a piece of heavy cardboard.The twist-tie that keeps a bread bag closed has a soft iron wire inside.

Magnetize the twist-tie by stroking it with one end of a magnet from the center toward one end several times as shown below.

A 4-inch square piece of heavy cardboard is required for the base. A straight sewing pin is required for the compass needle to pivot on. Draw a circle on the cardboard and mark it with the points of the compass as shown. Insert a straight pin from the back side of the cardboard.

Carefully measure the twist-tie and mark the center. Bend a flat-bottom “U” shape in the center as shown. The “U” must be deep enough so that the twist-tie can be balanced on the pin and turn freely without touching the cardboard. When you have successfully balanced the twist tie it should point north.

Electromagnetism can be demonstrated using items that can be found in many homes.

In 1820, Hans Christian Orsted turned on an electric current during an electrical demonstration and noticed that the needle of a nearby compass moved. He had just made one of the most important discoveries in the history of electricity. An electric current causes magnetism. Electromagnetism is used to operate electric motors, one of the most important uses of electrical energy.

Orsted’s discovery was accidental. His compass happened to be near a demonstration using electric current. After his initial accidental observation, he positioned his compass carefully for additional observations.

Replicating Orsted’s Discoveries

The following pictures illustrate some more careful observations using a dry cell battery, a piece of wire and a compass. To do this at home, any piece of metal wire can be used. Copper or aluminum would be best. Even a narrow strip of aluminum foil will work. The compass will be attracted to steel wire in the absence of an electric current, so steel wire may not work as well. A D-cell is shown in the pictures, but an AA-cell will work also. A triple A cell will probably work. The demonstration draws quite a bit of current, so it could deplete the smaller cells pretty quickly.

The wire in the first few pictures is an old piece of lamp cord that has deteriorated to the point hat it is no longer safe for it’s original use. It is fine for use in this demonstration. The cord has two conductors, but only one is needed, so the ends of the wire have been twisted together to avoid having to figure out which is which. The insulation at the ends of the cord has been scraped off with a knife.

Here, the compass has been positioned with the cord underneath arranged to match the direction of the compass needle. One end of the cord is under the dry cell, making contact with the negative end. If the battery is positioned too close to the compass, the compass needle may be attracted to the steel battery case.

When the free end of the wire is touched to the positive terminal of the battery, as shown below, the compass needle deflects. Note that the wire may get hot enough to make holding it to the dry cell uncomfortable.

The magnetic field surrounds the wire, so that the compass needle points in the opposite direction when it is under the wire. The compass needle would point at a right angle to the wire if not for the effect of the earth’s magnetic field. A higher current in the wire would make the needle angle closer to a right angle with the wire.

Here the wire is vertical, and three compasses show the magnetic field around the wire.

This picture shows how aluminum foil can be used instead of wire.

If you don’t have a compass, build your own. Another activity on this site shows how to do it.

… and how the very first electrical demonstration can be performed using materials found in every home.

Human knowledge of electricity began with lightning, electric fish and amber.

Lightning

Prehistoric people observed lightning in the sky during storms.  It made a bright light and a powerful noise. It could kill people and animals. It sometimes struck trees causing fire. It was once thought to be fire from the sky. It is now known that lightning is electrical.

Electric Fish

There are several types of fish and eels that can sting a person in a way that causes numbness in the area of the sting, but does not cause a wound. These creatures were known in prehistoric times but not understood. We now know that they have a special defensive organ that generates electricity.

Amber and The Very First Electrical Experiment

Amber is resin from trees that has solidified over time. It looks and feels like hard plastic. It was gathered and saved by ancient people for decorative objects and jewelry purposes. Some pieces of amber have insects trapped inside.

Ancient people discovered that, after amber is rubbed with animal fur, it has the power to attract light materials such as dust and small feathers (down). This was the very first electrical experiment.

The ancient Greeks called amber “electrum” after their name for the sun, “elector.” Thales of Miletus, one of the seven wise men of Ancient Greece was said to have believed that amber must contain life to have the power to move things. We know now that the force of amber is due to static electricity. William Gilbert gave us the word electricity by his use of the Latin word electricus to describe electrostatic phenomena as “amber-like.”

Electrical Charge

All matter is composed of atoms.  Atoms are composed of electrons, protons and neutrons. Electrons have a negative electrical charge, protons a positive charge and neutrons no charge. The protons and neutrons are tightly bound together to form the nucleus or center of the atom. The electrons are less tightly bound. The number of protons it an atom determines the atomic number and identity of the chemical element that it forms. Element number 1, Hydrogen has one proton. Element number 92 is Uranium with 92 protons.

Atoms in their “normal” state have an equal number of protons and electrons, so their positive and negative charges are balanced. That means that “normal” materials have no electrical charge. However, friction often causes electrons to transfer from one material to another. That is called the triboelectric effect. Some materials hold onto electrons more tightly than others. Amber holds onto electrons more tightly than cloth or animal fur, so when it is rubbed with those materials it tends to accumulate extra electrons and become negatively charged.  Feathers, pieces of hair, dry skin and other materials that make dust tend to leave electrons behind when they are separated from there origin. That gives them a positive electrical charge. That is why amber that has been rubbed by fur attracts dust and small feathers.

Triboelectric Series

The triboelectric series shows the relative tendencies of materials to become positively or negatively charged by friction. Rubbing together two materials that are far apart on this table results in the highest level of electrostatic charge.

Electrostatic Experiment

The first two of the following pictures re-create the ancient experience of picking something up using amber that has been rubbed by animal fur. The third picture shows how anyone can re-create this experience by rubbing plastic with cloth.

A piece of amber on rabbit fur

Dry lint picked up by a piece of amber that has been rubbed with rabbit fur

Dry lint picked up by a plastic bottle that has been rubbed with cloth