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PHYS142

  • A2-23: VECTOR PRODUCT

    A2-23
    Illustrate the product of two vectors
    The directions of the two vectors A and B, along with their vector product AxB can be illustrated using the model. The cross product can be adjusted in length, but not reduced to zero; its minimum length is shown in the photograph above.

    This is particularly valuable for understanding concepts such as torque or the Lorentz force.
    A2

    vec

  • J1-01 TRIBOELECTRICITY - CHARGING BY FRICTION

    J1-01
    Demonstrates "charging by friction"
    Rubbing silk on a glass rod makes the glass positive and the silk negative. Rubbing fur on a hard rubber rod makes the hard rubber negative and the fur positive. This effect is known as "triboelectricity," from the Greek "tribein," or to rub. The positively charged glass rod and the negatively charged hard rubber rod can then be used (1) simply to illustrate that electrical charge exists using an electroscope or (2) to perform other electrostatics experiments.
    J1b

  • J1-21 ELECTROSTATIC ATTRAC AND REPULS - CHARGED CYLINDERS

    J1-21
    Demonstrates electrostatic attraction and repulsion
    Charge the glass cylinders positive by rubbing with silk, and charge the hard rubber cylinder negative by rubbing with fur. The two positive glass cylinders repel each other, but both are attracted to the negative hard rubber cylinder.
    J1b

  • J1-24 ELECTROSTATIC HAIR RAISING

    J1-24
    Demonstrates electrostatic repulsion
    While standing on a large styrofoam insulating block, touch your hands to the top of the Van de Graaff dome, then have someone turn it on. The fact that your hair stands on end is a result of the repulsion between charges of the same sign that collect on your hair.
    J1a, OS2

  • 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

  • J3-02: ELECTRIC FIELD OF RING OF CHARGE - MODEL

    J3-02
    Aid in the visualization of the electric field of a ring of charge
    This is a non-working model for the electric field of a ring of charge. It shows explicitly the fields of two opposite segments of the charged ring, along with the vector sum of the two fields. This shows how two opposite sides cancel, leading to the field vector shown on the model.
    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

  • J3-13 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

  • J3-14 FLUX MODEL - ELECTROSTATICS

    J3-14
    Aid in visualizing flux at an angle through a surface
    Shows red flux lines and blue plane, oblique to the flux lines, represented by the blue vector area
    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

  • J3-23 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

  • J4-31 ENERGY STORED IN A CAPACITOR

    J4-31
    Demonstrates that energy is stored in a capacitor and how that energy may be used
    Three capacitors totaling 205,000 microfarads are charged to 15 volts. Closing the three switches one at a time (a) turn on the light, which decays exponentially, (b) turn on the bell, or (c) activate a motor which lifts the entire system up a few inches
    J4

  • 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

  • J4-51: THEREMIN

    J4-51
    Demonstrate the theremin
    A theremin is a musical instrument, invented in the early twentieth century by Russian scientist Dr. Theremin, which uses capacitance to change the pitch and the loudness of the sound. It was popular in dance bands in the first half of the twentieth century, and even used by The Beach Boys in the 1960s. By moving your hands up and down over the triangular capacitor plates on the top of the box, the frequency and loudness of the sound can be varied to produce a musical tune. Perhaps one of the most elegant examples of theremin music is the Rachmaninoff "Vocalise" performed by Clara Rockmore, the most well-known theremin artist ever, with Nadia Reisenberg on the piano. This music is on a CD, The Art of the Theremin, which will be found in our library of CDs in the "MUSIC" section of the demonstration storage.
    J4, ME3