Follow

Electric Fields and Potential

  • J4-12: ELECTROSTATIC FORCE - MOVING LUMBER

    J4-12
    Demonstrate polarization of water molecules.
    An eight-foot long pine 2x4 is balanced on a relatively friction-free support, so that it can rotate about the balance point. A rod charged by "friction" (either positive or negative) is held alongside either end of the 2x4. A force is exerted on the 2x4 and it rotates toward the rod, so that you can pull the 2x4 around with the rod. Changing to the other polarity rod creates the same force, and again the 2x4 can be pulled around by the rod. The non-uniform field of the rod lines up the polar water molecules in the wood and exerts an attractive force on them.
    OS0, J4

  • J4-13: MATCHSTICK ON NICKLE UNDER GLASS

    J4-13
    A simple trick easily solved with the application of electrostatic force and the polar nature of water molecules.
    A nickle is balanced on its edge in the center of a piece of paper, and a wooden match is balanced on the nickle. A plastic cup is placed upside down over the nickle and match, and a second nickle is balanced on bottom of the upside-down cup. The question is: how to remove the matchstick without disturbing either of the nickles? The answer lies in the polar nature of the water in the matchstick, which is affected by the presence of a nearby charged rod.
    J4

  • J4-24: FORCE ON DIELECTRIC IN ELECTRIC FIELD

    J4-24
    Demonstrate the force on a dielectric in an electric field.
    Two wire electrodes extend into a bath of dielectric oil, as seen in the photograph above. When a potential of 2500 volts is impressed between the wires a force is exerted on the dielectric in that region, causing the oil to rise between the two wires, as seen in the close-up photographs below.

    j4-24aj4-24b

  • K8-46: Radio Waves & Faraday Cage

    K8-46
    Demonstrates that radio waves do not penetrate a Faraday cage
    Tune the radio to an inoffensive station audible in the classroom. Then place the radio on a metal surface; the radio continues to play. Show students the cage and ask what will happen if you lower the cage over the radio. Note that they can still see through the cage, so light is passing through.

    Lower the cage over the radio. Once the cage surrounds the radio completely, it prevents RF waves from passing through, silencing the radio. This also shows the wavelength dependence of a Faraday cage; the much shorter wavelengths of the electromagnetic waves of visible light pass through the openings unhindered.
    K8

  • P4-05: PHOTOMULTIPLIER TUBE - LARGE

    P4-05
    Show them what a large photomultiplier tube looks like.

    This is a large (8") photomultiplier tube which was once used in a particle physics experiment. The photocathode surface (on the inside front face of the tube), the focusing electrodes, and the dynodes are all easy to see.

    The tube at the right is a small version of the type used in the Super Kamiokande project in Japan.

  • P4-41: RUTHERFORD SCATTERING MODEL

    P4-41
    Show difference in scattering from the Thompson and Rutherford models of the nucleus.
    Small ball bearings representing alpha particles roll down an inclined groove to gain kinetic energy, then pass through representations of either Thompsons model (center) of the nucleus or Rutherford's model (right) of the nucleus. The angle of the track or the starting position for the balls can be adjusted to change the energy of the alpha particles.

    p4-41ap4-41b

     

  • P4-51: MILLIKAN OIL DROP MODEL

    P4-51
    Demonstrate geometry for the Millikan oil drop experiment.
    This is a non-working model to illustrate the geometry of the Millikan experiment. A helium balloon tethered to the lower plate represents the oil drop. The plates are charged by the Wimshurst machine to create the electric force on the charged oil drop.