OR
Challenging STEM Activities Based on FUNdamental Science Concepts
Digital copies of this document can be obtained at: http://www.sciencescene.com. \
Developed by: Dr. Michael H. Suckley
Background:
In 1811, Danish schoolteacher Hans Christian Oersted discovered the first evidence of the relationship between electricity and magnetism. His discovery was quite accidental. Oersted laid a current-carrying wire beside a directional compass. As he did so, he noticed the compass needle turning. He immediately recognized that a magnetic field must have been emanating from the wire therefore causing the compass needle to be deflected. He also realized that the magnetic field had to be produced by the current flowing in the wire because, when the current was turned off, the needle ceased to be deflected. Oersted's discovery of the relationship between electricity and magnetism led to other discoveries:
1. Electric charges attract or repel one another.
2. Magnetic poles attract or repel one another.
3. An electric current in a wire creates a circular magnetic field around the wire.
4. A current is induced in a loop of wire when it is moved towards or away from a magnetic field, or a magnet.
By applying Oersted’s key principles and developing additional principles Michael Faraday was able to make a functioning electric motor in 1832. This handout presents the application of Oersted and Faraday’s discoveries in the making of simple motors which have three components, the battery, a piece of wire and a magnet. Using these variables eight different motors will be made that can be used for student research projects. These motors illustrate thesame physics that are found in all electric generators and electric motors today and are remarkably inexpensive to build.
Please note: Magnets have been known to cause injury or even death if swallowed. Do not allow magnets to snap together, or snap against metal objects, as they are easily chipped. Magnets are also capable of nipping your skin if allowed to snap together.
Basic Electric Motor
Materials
· 1 AA battery
· 29.0 cm #26 wire
· 2 1.25 cm pieces of Duct Tape or #27 rubber bands
· 2 paperclips
· 1 magnet
· 1 1.5x4.0 cm Cardboard with double stick tape
Procedure
1. The armature supports are made out of two paperclips. Unbend the paper clips by lifting and rotating one end to form a small loop in the center of the paper clip. The loop can be made larger by inserting a toothpick while bending.
2. Use tape or a #27 rubber band to hold the paper clips on the ends of the battery. When using the rubber band place the rubber band around the battery, lengthwise, and then insert the paperclips. Make sure paperclips are attached so that they are level.
3. Place a piece (1.5-cm by 4.0-cm) of self-stick tile or cardboard with double-sided tape to the bottom of the battery for support.
4. The armature is made by wrapping 30 cm. of #26 insulated enameled copper around a AA battery. Wrap the ends of the wire around the coil two times tightly, leaving the ends sticking out like handles. Hold one end of the armature in each hand and spin adjusting making sure that the coil is balanced and rotating smoothly.
5. The wire used to make the armature has a coating on it. This coating must be carefully removed to allow the electricity to flow. You can either scrape or use sandpaper to remove the insulation. Scrape off all the coating at one end and the top surface only at the other end. Scrape off enough length of the wire so that the scraped area can make contact with the armature supports placed on the battery. Remember: make sure that the coil is balanced and rotates smoothly.
6. Place the armature in the paper clip supports. Make sure that the scraped area of the armature touches the paper clips. If the scraped area of the armature does not touch the paper clips readjust or re-scrape the wire.
7. Finally, place the magnet on the top of the battery, and center the coil over it. If everything is just right, giving the coil a little spin will cause it to start rotating.
8. Rotate and/or adjust the loop until it begins to work. Don't fret if it doesn't work the first time. This simple motor can be a bit finicky to get working, and you will probably have to adjust the end of the wires a bit until the coil is balanced.
Basic Electric Motor Explained
The paperclips and wire create a closed loop circuit that can carry current. Current flows from the negative terminal of the battery through the circuit, to the positive terminal of the battery. The current travels through the coil which is called the armature of the motor. This current induces a magnetic field in the coil.
Magnets have two poles, North and South. North-South interactions stick together, whereas north-north and south-south interactions repel each other. Because the magnetic field created by the current in the wire is not perpendicular to the magnet on the battery, at least some part of the wire’s magnetic field will repel and cause the coil to continue to spin.
The insulation was removed from only one side of the wire to make a break in the circuit. The current causes the magnetic field to pulse on and off producing the rotation of the coil. Whenever the current is moving through the coil it produces a magnetic field. The coil is repelled by the stationary magnet’s magnetic field. When the coil isn’t being actively repelled (during those split second intervals where the circuit is switched off), momentum carries it around until it’s in the right position to complete the circuit, induce a new magnetic field, and be repelled by the stationary magnet again. Once moving, the coil will continue to spin until the battery is dead.
Make Motors Pg. 2