Demonstrate Magnetic Fields, Electric Current, and Basic Principles of the Motor
In 1820, Danish physicist/chemist Hans Christian Ørsted (Oersted) noticed that when current from his Voltaic pile was switched on and off, a compass needle placed near the wire deflected from true magnetic north. Within a few months of careful study, he deduced that a magnetic field circles a current-bearing wire.
It was not long before scientists and inventors found practical applications of this discovery. In 1821, English physicist/chemist Michael Faraday made brilliant use of two fundamental principles: 1) magnetic fields circle current-bearing wire, and 2) magnetic fields interact with other magnetic fields. He found that the magnetic fields around a permanent magnet and a current-bearing wire could be made to interact and cause motion. This was essentially the first electric motor, and modern motors still operate on this same principle.
Faraday used wire, a battery, a permanent magnet, and a dish of mercury to make his first motor. When current flowed through his circuit, the magnetic field induced around the wire that hung free in the mercury interacted with the magnetic field around a permanent magnet placed within the mercury. This interaction caused the free wire to rotate around the permanent magnetic whenever current flowed through the circuit.
It is fairly simple to construct a working motor similar to Faraday's original motor that will amaze your students. Due to safety concerns, salt water is substituted for mercury.
Materials: plastic 2L bottles, connecting wires, modern Voltaic pile (i.e., 9V battery), neodymium magnets, salt water, tape, modeling clay, stiff copper wire, aluminum foil, 2 small paper clips, plastic straw, switch (optional)
Construction: Cut one 2L bottle approximately 4 in tall. Place some modeling clay in the bottom of the bottle. Place a stack of neodymium magnets in the tub. Standard steel bar magnets are likely not strong enough. Fill with salt water. Tape the straw to the top of the second 2L bottle. Place stiff copper wire through the straw and attach the paper clips to a hook bent on the end of the wire. The paper clips will serve as a swivel and allow free movement of the hanging stiff cooper wire around the stack of magnets. Connect the other end of the top wire to one terminal of the 9V battery. Connect the other terminal of the 9V battery to the switch. Connect the switch to a folded over piece of aluminum foil. Place the other end of the aluminum foil in the salt water. Connect the other stiff copper wire to the swivel so that it rests in the salt water near the magnet stack. Close the switch and observe the copper wire. Reverse the battery terminals and notice any change in the motion. Turn the stack of magnets over and notice any change in the motion.
Thank you to Dr. Joel Bryan of Ball State University in Muncie, IN for authoring this article and video.