Magnetism

  1. Magnetism is different from electricity: magnetic objects are uncharged.
  2. All magnets have "north" and "south pole": like poles repel, unlike poles attract.
  3. One can not find a mono-pole magnet. If you cut a magnet in halve, you will get two weaker magnets with two poles, not a mono-pole magnet.
  4. Magnetic field lines show direction of the magnetic force. Magnetic field lines always go from North pole to South pole and close on themselves without stopping or starting.
  5. Earth has magnetic a field of its own, which is related to Earth’s rotation about its axis.
  6. Compass needle is a small magnet that shows direction of the magnetic field.

The Connection between Electricity and Magnetism

  1. Magnetic field due to currents.

    In 1820 Oersted observed that a moving electric charge (electric current) produces a magnetic field in the space around it.

  2. Magnetic force on moving charges (currents.)

    Observation: A magnetic field (external) exerts a force on a moving electric charge (current). i.e. cosmic rays

    http://www.youtube.com/watch?v=tUCtCYty-ns

  3. Electromagnetic induction

Observation: A moving magnet produces an electric field in the space around it. Faraday, 1830. http://www.youtube.com/watch?v=hajIIGHPeuU

    1. Thus a moving magnet induces a current in a coil of wire, if one moves relative to another.
    2. Changing magnetic field produces electric field.
  1. Electromagnetic gadgets
    1. Electric generator
    2. Electric motor
    3. Transformer