Electromagnetism: Magnetism from Electricity
In 1820, Danish physicist Hans Oersted (1777–1815) noticed that a compass needle was deflected at right angles to a wire carrying an electric current. Since a compass needle is deflected by a magnet, he concluded that the electric current somehow caused a magnetic field around the wire. Further studies by Oersted proved that any wire carrying an electric current has a magnetic field around it. Oersted's discovery started the study of electromagnetism (relationship between magnetic fields and electric currents) and the use of an electromagnet (device that uses an electric current to produce a concentrated magnetic field).
In this project, you will determine the direction of a magnetic field around a current-carrying wire. You will determine the effect of the direction of an electric current in a current-carrying wire on the pattern of the magnetic field around it. You will also make an electromagnet, determine its polarity, and test its strength.
Purpose To determine the direction of a magnetic field around a current-carrying wire.
- sheet of copy paper
- l.5-volt D battery
- wire stripper
- 12-inch (30-cm) piece of 20- or 22-gauge insulated single-strand wire
- Use the pencil and the ruler to draw two perpendicular lines across the center of the paper. Label the longer line N, S and the shorter one E, W (as shown in Figure 20.1).
- Place the paper on a wooden table and set the compass in the center of the paper, where the lines cross.
- Allow the needle to come to rest in line with Earth's magnetic field.
- First rotate the compass so that N on the compass is in line with the needle pointing north. Then lift the compass and rotate the paper so that its compass directions match those on the compass. Replace the compass on the paper.
- Place the battery on the east side of the paper, with the negative terminal of the battery pointing south.
- Using the wire stripper, remove about 1 inch (2.5 cm) of insulation from each end of the wire.
- Bend the wire so that it has a straight center piece slightly wider than the battery's length.
- Holding the insulated part of the end of the wire, position the wire so that the center section is about 1 inch (2.54 cm) above the compass and across the compass from north to south. Then touch the bare ends of the wire to the ends of the battery for about 1 second. Notice the direction in which the north end of the compass needle moves. CAUTION: For your safety, hold the insulated part of the current carrying wire so that you do not get burned or shocked. Holding the wires against the battery terminals for longer than 3 seconds can result in the wire becoming hot enough to burn your skin.
With the battery's negative terminal pointing south and the battery on the east side of the compass, the north end of the compass needle deflects from its north position toward the east.
The direction of the current in the wire is from the battery's negative terminal to its positive terminal. Current in the wire produces a magnetic field. With the current flowing in a south-to-north direction, the magnetic field below the wire is toward the east, as indicated by the deflection of the north end of the compass needle toward the east. The relationship between a magnetic field and an electric current is called electromagnetism.