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 Subject: Magnetism Category: Science > Physics Asked by: rob1981-ga List Price: \$5.00 Posted: 23 Jan 2003 10:10 PST Expires: 22 Feb 2003 10:10 PST Question ID: 147525
 ```If moving a conductor through a magnetic field induces an electric current, will applying an externally sourced current to a conductor in a magnetic field make the conductor move?```
 ```Hi Rob, The short answer to your question is yes, a current flowing through a conductor in a magnetic field will induce a force upon the conductor which, assuming the conductor is not fixed, will cause it to move. Common applications of this are the electric motor and loudspeaker. Given a constant magnetic field strength and electric current, the force induced is proportional to the component of the current flowing perpendicularly (at 90 degrees) to the magnetic field. In other words, if the wire carrying the current is running in the same direction as the magetic field then no force will be induced. Equally, if the wire is completely perpendicular to the direction of magnetic field, then the force will be at a maximum value. A simple diagram of this is available in section 2 of: Audio Systems http://www.acoustics.salford.ac.uk/acoustics_world/id/Loudspeakers/Loudspeakers.htm As stated by the site above, the size of the force induced in Newtons, F = Bil sin(theta) where B is the magnetic flux density (in Webers), i is the current flowing through the wire (in amps), l is the length of the wire in the field (in metres), and theta is the angle of the wire witrh respect to the direction of the magnetic field. The direction of movement of the conductor can be determined throught the use of Fleming's Left Hand Rule. By positioning one's left hand as shown in the diagram in the Audio Systems page ( http://www.acoustics.salford.ac.uk/acoustics_world/id/Loudspeakers/Loudspeakers_files/image021.gif ) with the first finger pointing in the direction of the magnetic field and the second finger in the direction of current flow (conventionally positive to negative), the thumb will point in the direction of movement of the conductor. A simple explanation of why the conductor moves is available from GCSE Bitesize: Physics http://www.bbc.co.uk/schools/gcsebitesize/physics/electricity/electromagneticforcesrev6.shtml If you would like a more complex and in depth discussion of the physics involved this article may be of interest: Motors and Generators http://science.uniserve.edu.au/school/curric/ stage6/phys/stw2002/khachan.pdf Further links: Electric Motor: The Motor Effect http://www.schoolscience.co.uk/content/4/physics/copper/copch3pg2.html Science Snacks: Motor Effect http://www.exploratorium.edu/snacks/motor_effect.html I hope this answers your question fully; if you would like any further clarification please ask before rating my answer. Thanks, mcfly-ga :) Search strategy: induced current physics fleming left hand rule how "electric motor" works how loudspeaker works``` Clarification of Answer by mcfly-ga on 23 Jan 2003 12:16 PST ```Apologies for the unusual formatting in places in my answer - Notepad seems to have developed a mind of its own!```
 rob1981-ga rated this answer: `Very concise and explicit, thanks.`