Motors

We generally understand that magnets attract metal objects, that they have poles (North & South) and that these poles interact so that opposites attract and like poles repel one another. It is also important to know that between these poles there is a magnetic field that runs from the North to the South pole in the form of curved lines The magnets we are using are button magnets. They still have North and South poles which are assigned to the flat surfaces of the magnet with the field still running from North to South. Electrical current is produced by the movement of electrons through an object that is conductive. The flow of electrons in a battery is out of the negative end, into the positive terminal, and back through the battery to the negative in a loop (figure c). When there is no outside connection, the battery does not produce a current because it is an open circuit. When the circuit is closed by plugging the battery into an object such as a flashlight, the electrons are able to flow from the negative terminal, through the object being powered, and back into the positve terminal and through the conductive solution inside the battery over and over in a loop until the electrons are no longer able produce the needed energy. The homo-polar motor works due to Lorentz-force. Lorentz-force explains the force that results from the velocity (movement and direction) of charged particles through a magnetic field. The closer the current and magnetic field are to being at a right angle (90 degrees), the stronger the force that will put on the screw in the basic motor, or on the wire in the upgraded version. The model below is used to show direction of the force (Figure D). The V or current arm would be moved in the direction of current flow, with the B or magnetic field arm pointing in the direction of the field. By manipulating these arms to model the directions of the current and field at the same time, the force arm with demonstrate the direction of the force resulting from the interaction. This can be easily modeled and used for exploration by making a three dimensional model with dowels or popsicle sticks. The wire is used to create a path for the current to return from the positive terminal to the negative terminal of the battery, closing the circuit. This essentially short-circuits the battery and causes it lose its charge rather quickly (approximately 2 minutes with a mid-quality battery if allowed to run without stopping). The interaction between the magnet’s field and the current from the battery will result in a torque (twisting) force on the magnet that will run either clockwise or counterclockwise depending on the flow of the current. (If you switch the magnets to the positive terminal with the wire bend (or screw) on the negative terminal, it will spin in the opposite direction. CREDITS Special Acknowledgement is given Dr. Patrick Leclair, Professor of Physics at the University of Alabama, Tuscaloosa. Special Assistance and mentoring by Dr. Patrick Leclair and Dr. Nouredine Zettili, Professor of Physics at Jacksonville State University, Jacksonville, Alabama. Homopolar Motor Image Credits: 1. Wohba Online- http://wohba.com/blogimages/motor0307.jpg 2. Dangerously Fun Online- http://dangerouslyfun.com/images/photos/homopolarmotor2.jpg. Image Credits: Figure A- Magnetic Shield Corporation- http://www.magnetic-shield.com/faq/interference.html Figure B- Modified version of figure A Figure C- Rayovac Corporation- http://www.rayovac.com/wizard/battery_howwork.htm Figure D- Newton Satellite School Page- http://www.sr.bham.ac.uk/xmm/fmc1.html Figure E- Evil Mad Scientist Online- http://www.evilmadscientist.com/article.php/SimpleMHD