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PHYS122

  • J1-25 VAN DE GRAAFF - TRAINED RABBIT

    J1-25
    Demonstrates electrostatic repulsion
    A piece of fur, the "rabbit," is placed on top of the Van de Graaff dome, and a grounded point is held adjacent to the dome as the Van de Graaff is turned on. Pull the point back, allowing the dome and fur to charge, while ordering the rabbit to "sit up." Move the point closer to the dome while ordering the rabbit to "sit down."
    J1a, J1b

  • J1-26 VAN DE GRAAFF - REPULSION OF PIE PANS

    J1-26
    Demonstrates electrostatic repulsion

    A group of aluminum pie pans is placed on top of the Van de Graaff dome and the Van de Graaff is turned on. The pie pans are pushed off the top of the dome one at a time by the electrostatic repulsion. Use this as a way to argue that electrostatic forces might be stronger than gravitational forces.

    Engagement Suggestion:
    • Before turning the generator on, encourage students to predict what is going to happen. Challenge them to explain their hypotheses in terms of what they have learned about the behaviour of electrical charge.
    • Feel free to invite students to collect the scattered pans, but remind them not to get close to the Van de Graaff while it is turned on.
    J1a

  • J2-01: WIMSHURST MACHINE

    J2-01
    Generate high electrostatic potentials.
    Cranking the handle rotates the two plates in opposite directions, generating a large electrostatic potential. The Leyden jars can be charged to increase the intensity of the spark between the two balls on the arms mounted above the Leyden jars. This machine can also be used for other demonstrations requiring high potentials. This gizmo may go up as high as 500,000 volts.
    J2a

  • J2-03 VAN DE GRAAFF GENERATOR WITH GROUND SPHERE

    J2-03
    Demonstrates the operation of a Van de Graff generator and illustrates electrostatic concepts
    The ground sphere is positioned a few inches away from the Van de Graaff dome and grounded to the base of the Van de Graaff. When the machine is turned on, the dome becomes charged negative and the ground sphere becomes charged positive by induction. The ground sphere is attracted to the dome, as can be easily seen. After the spark, the two spheres lose their charges, and the ground sphere relaxes to its original position, whereupon the cycle repeats. See below for a paper by Dr. R. Berg on the fabrication and maintenance of the belt.
    J2a

  • J2-14 LIGHTNING ROD SIMULATOR

    J2-14
    Demonstrates how lightning rods really work
    A ground sphere is positioned adjacent to the Van de Graaff generator so that the ground sphere is charged by induction and creates large sparks. While this system is working, a grounded point is aimed at the Van de Graaff dome from a distance of several times the distance between the dome and the ground sphere. The grounded point discharges the dome at a much lower potential, preventing buildup of charge on the ground sphere and the concomitant spark discharge.
    J2a

  • J2-33: TESLA COIL - PORTABLE

    J2-33
    Easy-to-use high-voltage device for use in various demonstrations or just to draw a nice spark.
    This is an easy-to-operate 110V/60Hz device that reliably produces a nice spark. It can be used to demonstrate discharge to grounded objects. Please handle carefully.
    J2b

  • J3-01: EXISTENCE OF ELECTRIC FIELDS

    J3-01
    Demonstrate the existence of electric fields and to map them semi-quantitatively.
    A small conducting sphere on an insulating pole is connected electrically to an electroscope. The strength of the electric potential can be mapped out by observing the deflection of the electroscope as the metal ball sensor is moved about in the region of the Van de Graaff dome. After drawing a spark the electroscope must be grounded to reset it to neutral potential.
    J3a, J3b, LS1

  • J3-07: VAN DE GRAAFF - DISCHARGE TO VARIOUS RADII

    J3-07
    Demonstrate that for a charged conductor a smaller radius produces a higher electric field.
    The Van de Graaff discharges to the ground sphere at the left in the absence of the smaller elliptical conductor (from J3-06) at the right. When the grounded elliptical conductor is positioned near the Van de Graaff dome, the end with the smaller radius of curvature discharges the dome with less of a spark, indicating a smaller electric field. Discharge to the larger end is more similar to the ground sphere.
    J3a, J3b

  • J3-08 VAN DE GRAAFFS - INTERACTING FIELDS

    J3-08
    Shows field lines for two identical charges
    The two Van de Graaffs are turned on briefly to charge them to the same potential. (They may be touched together to assure that the potential is the same magnitude.) The tissue streamers indicate the paths of electric field lines, which are radially outward for isolated charges. When the two domes are brought together, the inner field lines are pushed away from each other
    J3a

  • J3-11: EQUIPOTENTIALS/LINES OF FORCE - ONE CHARGE

    J3-11
    Aid in visualization of equipotentials and lines of force.
    A positive point source is located at the center of the model. The vertical height of the surface represents the potential; the white lines are equipotentials. The blue lines represent lines of force.
    J3b

  • J3-13 POTENTIAL SURFACE MODEL WITH E FIELD VECTORS

    J3-13
    Illustrates the relationship between the electrostatic potential and the electric field
    The white styrofoam surface represents a potential surface, with the closed lines encircling it being the equipotentials. The electric field vectors at various points on the surface are represented by the vectors sticking out from the surface. These vectors are quantitatively correct for this surface.
    J3b

  • J3-21 FARADAY CAGE

    J3-21
    Demonstrates that the electric field within a closed conducting surface is zero
    When the cage is charged, the aluminum foil "pith balls" move away from the outside of the cage, indicating the presence of an electric field. However, on the inside of the cage the pith balls do not move away from the wire cage, indicating that there is no charge and therefore no electric field on the inside of the conducting surface.

    Note that this is most easily charged with the charging materials from J1-01.
    J3, J1

  • J3-22: FARADAY CAGE - ELECTROSCOPE

    J3-22
    Demonstrate that the electric field within a closed surface is zero.
    Charge the two wire strainers with triboelectric materials (J1-01), which are connected electrically to the electroscope indicator. With the two meshes separated, the electroscope deflects. When they are placed together, forming a closed sphere, the electroscope deflection is zero, indicating zero electric field within the closed cage. The charge that was originally on the electroscope has flowed to the outside of the conductor. Note that if you then re-open the two hemispheres, the electroscope again deflects as the charge flows back into it. An alternative way to use this demo is to bring the wire strainers near to a charged van de Graaff, first open, then closed. The difference in this case is that the electric field being shielded is fully external to the device, in contrast to the first method where it was an internally generated field.

    This is best used with a light source to project the shadow of the electroscope needle through the mesh onto the wall.
    J3, J1

    j3-22a

  • J3-23 FARADAY CAGE - RADIOWAVES

    J3-23
    Demonstrates that radio waves cannot penetrate a Faraday cage
    The radio is tuned to a good station so that everyone can hear. Lowering the screen Faraday cage over the radio stops the radio waves, and the sound of the radio ceases.
    K8

  • J3-24 HOLLOW CONDUCTING SPHERE

    J3-24
    Demonstrates that charge resides on the outside surface of a conductor
    Charge the sphere several times by scraping charge off a rod, either positive or negative. Touch the proof plane several times to the outside of the sphere and then to the electroscope. The electroscope charges, indicating that there is charge on the outside of the sphere. Touch the proof plane several times to the inside of the sphere and then to the electroscope. The electroscope does not charge, indicating that there is no charge on the inside of the sphere. Repeat for the outside to demonstrate that the sphere is still charged.
    J3

  • J4-01 PARALLEL PLATE CAPACITOR

    J4-01
    Demonstrates that potential difference across a capacitor is proportional to the plate separation

    This simple parallel plate capacitor consists of two large aluminum plates with an air gap. The parallel plate capacitor is charged to 1000 Volts using a low-current DC power supply by pressing a switch. The plates may then be separated and the voltage observed using the electrometer, demonstrating that the voltage is proportional to the plate separation.
    Engagement Suggestion
    • You can show that the voltage across the capacitor varies with the spacing if the charge is held constant (i.e. the power supply is not connected), or you can show how the capacitance varies with the spacing if the power supply remains connected. Note that this remains linear only within a limited distance regime.
    J/K

  • J4-04 PARALLEL PLATE CAPACITOR - IONIZATION OF AIR

    J4-04
    Demonstrates the mobility of ions
    Charge the capacitor and separate the plates. Bring a lighted match under the volume between the two plates. The ionization of the flame creates free positive and negative charges which migrate to the capacitor plates, quickly discharging the plates.
    J/K

  • J4-22 PARALLEL PLATE CAPACITOR WITH DIELECTRIC

    J4-22
    Demonstrates that inserting a dielectric into a capacitor increases the capacitance
    The parallel plate capacitor is charged by the power supply and the plates are separated, increasing the voltage between the plates. A thick dielectric sheet inserted between the plates of the capacitor results in a decrease in the voltage between the plates. Because the charge on the plates remained constant, this means that insertion of the dielectric has increased the capacitance. This allows more charge to be stored by the capacitor at the same voltage.
    J/K

  • J4-32 DISCHARGE OF CAPACITOR WITH BANG

    J4-32
    Demonstrates that capacitors store electrical energy
    A 3500 microfarad capacitor is charged to 100 volts using the battery pack. Touch the capacitor terminals to the copper contacts on the battery pack; check that the polarity is correct, this is an electrolytic capacitor. Discharging the capacitor with the large screwdriver produces a very loud BANG.
    J4

  • J4-41: CAPACITORS

    J4-41
    Display a variety of capacitors
    Just a bunch of different kinds of capacitors. Just lying there.
    J4