Saturday, January 21, 2012

Magnetism: Right Hand Rule #4

Brief History
  • In 1820, Ampere showed that a constant current could produce a constant magnetic field
  • In 1832, Michael Faraday tried to prove that a constant magnetic field could produce a constant current. However, during his experiment, he found out that it was only when the magnetic filed was changing that current was produced. This was how alternating current (AC) was discovered.
General effect
Moving a magnet toward a copper ring will induce a current in the copper ring. However, once the movement is stopped, the current will disappear

Right Hand Rule #4
(Unfortunately, I do not have enough time to make a picture)
With an open palm:
  • Thumb points toward the relative motion of the copper ring or coil (the magnet is the reference point).
  • Fingers point toward the direction of the magnetic field has it crosses the copper ring
  • Out of the palm is the direction of the current
Lenz's Law
Using the law of energy conservation, Heinrich Lenz showed that the induced current produced would always produce a magnetic field that would oppose the motion of the coil. So for example, if the north pole of a magnet approaches a coil, this is what would happen: