Lecture 14

Summary

Force between parallel wires
Solenoids

Currents & magnetic fields video
Faraday's Law
- steady field & stationary charges
- definition
- demonstrations
  - magnet through wire loop applet
    
    Example #1
  - jumping ring
  - generators applet
Lenz's Law
- definition
- demonstrations
  - jumping ring
  - rail guns
  - roller coaster photo
  - superconductor levitation photo
  - magnetic levitation train photos

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Current is produced in a loop when a magnet is moved into the loop. Where does the electrical energy come from?
A. Energy stored in the wire atoms.
B. Energy stored in the magnet
C. Energy in the magnet's motion.
D. Energy in electric waves.
Answer

C. Energy in the magnet's motion.
Because of Lenz's law a person must do work in order to shove a magnet into a wire loop against the opposing field created by the induced electrical current. Faraday's law therefore describes how kinetic energy can be converted into electrical energy. This is the foundation of how an electrical generator works.

Vertical Velocity (or V2) is an Impulse Coaster at Six Flags Great America which is a coaster that is launched forwards and backwards using electromagnetic motors. You can see the magnets above the track as this trainload of riders is launched out of the station. The first launch is quite a rush and you get going faster and faster as you go forwards and backwards until you get up to 70 miles per hour.

A magnet is suspended above a superconducting pellet because the induced currents on the surface of the superconductor create a magnetic field that opposes the magnet's field by Lenz's Law. The phenomenon is best described by the Meissner Effect.

Images of magnetically levitated trains on test tracks in Japan.

Picture (600x300, 70.2Kb)