Activity 3
The Electricity and Magnetism Connection
Background Information
Electricity and magnetism are intimately related. To make a magnetic field, run electric current through a wire. To put a force on an electric charge, move the charge in a magnetic field. To make a current, move a wire in a magnetic field. Such phenomena led physicists to the term electromagnetism to express the relationship between electricity and magnetism.
Any electric current has an associated magnetic field. For a long, straight wire, the magnetic field makes concentric circles around the wire. As distance from the wire increases, the field becomes weaker. To make a stronger field, bend the wire into a loop.
Notice how the field from opposite sides of the coil reinforces inside the loop. At large distances, the field of this loop is the same as the field from a bar magnet. If the loop is a coil of wire (with many turns), the strength of the field is proportional to the number of turns of the coil.
A changing magnetic field through a loop of wire induces a current in the wire. Moving the loop near a magnet produces such a changing field (because the magnetic field is not uniform). Through this process, which is called current induction, generators in power plants produce electricity. Current induction depends only on relative motion, as the students discover in this activity. They wind a coil to increase the strength of the induced current (just as a coil increases the strength of the magnetic field produced by a current-carrying wire). Whether they leave the coil at rest and move the magnet into the coil, or leave the magnet at rest and move the coil around the magnet, current is induced just the same.
Magnetism is a collective phenomena. The individual atoms of many elements are magnetic. In certain metals, such as iron, neighboring atoms interact so that their atomic magnets line up, a phenomenon called ferromagnetism. The result is the formation of many small regions of magnetism called domains in the piece of iron. These domains point in various directions, so their magnetism cancels out. But if the piece of iron is placed in a magnetic field, the domains line up, their magnetic fields reinforce, and the iron becomes a permanent magnet.
In Step 12, students connect several batteries in series to increase the current through the electromagnet. Increasing the current will increase the strength of the electromagnet, since more of the domains mentioned above will be lined up. But there is a limit to this increase, because once all the domains are lined up, no further magnetism can be obtained from the nail. This effect is called saturation.
The Electricity and Magnetism Connection
Background Information
Electricity and magnetism are intimately related. To make a magnetic field, run electric current through a wire. To put a force on an electric charge, move the charge in a magnetic field. To make a current, move a wire in a magnetic field. Such phenomena led physicists to the term electromagnetism to express the relationship between electricity and magnetism.
Any electric current has an associated magnetic field. For a long, straight wire, the magnetic field makes concentric circles around the wire. As distance from the wire increases, the field becomes weaker. To make a stronger field, bend the wire into a loop.
Notice how the field from opposite sides of the coil reinforces inside the loop. At large distances, the field of this loop is the same as the field from a bar magnet. If the loop is a coil of wire (with many turns), the strength of the field is proportional to the number of turns of the coil.
A changing magnetic field through a loop of wire induces a current in the wire. Moving the loop near a magnet produces such a changing field (because the magnetic field is not uniform). Through this process, which is called current induction, generators in power plants produce electricity. Current induction depends only on relative motion, as the students discover in this activity. They wind a coil to increase the strength of the induced current (just as a coil increases the strength of the magnetic field produced by a current-carrying wire). Whether they leave the coil at rest and move the magnet into the coil, or leave the magnet at rest and move the coil around the magnet, current is induced just the same.
Magnetism is a collective phenomena. The individual atoms of many elements are magnetic. In certain metals, such as iron, neighboring atoms interact so that their atomic magnets line up, a phenomenon called ferromagnetism. The result is the formation of many small regions of magnetism called domains in the piece of iron. These domains point in various directions, so their magnetism cancels out. But if the piece of iron is placed in a magnetic field, the domains line up, their magnetic fields reinforce, and the iron becomes a permanent magnet.
In Step 12, students connect several batteries in series to increase the current through the electromagnet. Increasing the current will increase the strength of the electromagnet, since more of the domains mentioned above will be lined up. But there is a limit to this increase, because once all the domains are lined up, no further magnetism can be obtained from the nail. This effect is called saturation.