|MadSci Network: Physics|
Hello Marianne, Hopefully I can shed some light on the right and left hand rules. First, who _was_ this Fleming guy? Sir John Ambrose Fleming lived 1849-1945 in England and was an electrical engineer. Most of his work was in electric lighting and telegraphs. He developed some of the first electric ship lights, but he is most noted for developing the vacuum diode- a device that converts an alternating current radio signal to a direct current that can be used in a telephone receiver. You can learn more about Fleming at one of the on-line encyclopedias such as www.britannica.com. Now on with the right and left hand rules. They are handy ways to remember the relationship between magnetic field, current, and the resulting force on the conductor (or motion if it's allowed to move). Finger positions: for the right-hand rule, if you hold your right hand so that you point your index finger to something in front of you, have your thumb pointing toward the ceiling, and second (middle) finger to the left so that each finger is perpendicular to the other two. The same finger finger positions on the left hand are used for the left-hand rule. An electric motor is very simply a loop or coil of wire that is free to rotate in a magnetic field. When there is a current in the wire, a magnetic field is generated which will want to align itself with the external magnetic field. This causes the loop to want to rotate. For this we use the LEFT hand rule to determine the direction of the force on the wire and hence which way the motor will turn. If your fore finger points along the magnetic field and the central finger along the direction of the current, then the thumb points along the direction of motion of the conductor. A dynamo or generator is essentially a type of electric motor which has permanent magnets in it to provide the magnetic field. Instead of supplying a current to the coil and getting rotational motion of the shaft in return, you supply rotational motion and get a current in return. In this case the RIGHT hand rule can be used to determine the direction of the current flow in the wire loop. If your fore finger points along the magnetic field and the thumb points along the direction of motion of conductor, then the central finger would give us the direction of the induced current. I checked what my fingers represented in the CRC Handbook of Chemistry and Physics to make sure I was right (or left?) Good luck, Drew
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