23.5 Electric Generators

23.5 Electric Generators

  • Roller coasters use rows of rare earth magnets for magnetic braking.
    • The pot and its contents increase in temperature when the magnetic field is varied rapidly.
    • The base of the pot needs to be ferromagnetic, iron or steel in order for the pot to work.
  • Consider the following example.
  • The coil is in a uniform 1.25 T magnetic field and has a 5.00 cm radius.
  • The emf is caused by the magnetic flux changing from its maximum to zero when this generator coil is rotating through one-fourth of a revolution.
  • Similar to the 120 V used in household power, this is a practical average value.
  • It depends on the angle between the magnetic field and the coil.
  • A generator with a single rectangular coil rotating at constant angular velocity in a uniform magnetic field produces an emf that varies in time.
    • The generator is similar to a motor, except the shaft is rotating instead of the other way around.
  • The magnetic force on the wires of the loop causes them to move.
    • Currents can be caused by charges parallel to the wire.
    • The force of the wire does not cause a current for those in the top and bottom segments.
    • The side wires can be used to find the emf.
  • The motional emf is determined by the magnetic field and the velocity v. The emf on each side is the same as the one on the other side.
  • The expression does not give emf as a function of time.
    • The time dependence of emf can be found by assuming the coil rotates at a constant angular velocity.
  • Linear velocity is related to angular velocity.
  • The period is and the Frequency is.
  • A light bulb with the system of rings and brushes shown is the emf of a generator.
    • The emf of the generator is determined by the graph.
  • Where is the period?
    • The script E stands for emf.
  • It makes sense that the peak emf is.
    • The greater the emf, the quicker the generator is spun.
    • At least the cheaper ones are noticeable.
    • One of the authors as a juvenile found it amusing to ride his bicycle fast enough to burn out his lights, until he had to ride home lightless one night.
  • The scheme in Figure 23.23 shows how a generator can be made.
    • More elaborate arrangements of multiple coils and split rings can produce smoother DC, although electronic means are usually used to make ripple-free DC.
  • In this configuration, split rings produce a DC emf output.