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PHYS272

  • C7-11: COLLISIONS OF BALLS - EQUAL MASSES

    C7-11
    Demonstrates conservation of energy and conservation of linear momentum in multiple elastic collisions
    Hold one, two, three, or four balls to the side and release. Symmetric oscillations result from conservation of energy and conservation of linear momentum in the collision sequence.

    Click here to go to a simulation of this device by Erik Neumann.
    C7

  • C7-12: COLLISION OF BALLS - ONE LIGHTER MASS

    C7-12
    Show what happens when one mass in a collision ball set is different from the others.
    The collision ball sets photographed are identical except that the fourth ball from the left in the set on top is lighter - the original steel ball has been replaced by one made of aluminum (It is slightly less shiny.). Q: Will the set with one lighter ball work the same as the "normal" set if one ball is picked up and released? A: No. Momentum and energy are transferred in a series of elastic collisions between two balls at a time; for identical balls all the momentum and energy are transferred from one ball to the next in each collision. The lighter mass ball breaks the chain, at which point there is no longer complete transfer of all the energy and momentum to the next ball.
    C7

  • C7-17 SUPERBALL

    C7-17
    Illustrates nearly elastic collisions
    Drop the superball and watch it bounce
    C7

  • C7-18 COLLISIONS OF BALLS - ASTROBLASTER

    C7-18
    Shows velocity multiplication in colliding balls

    This device has four balls of graduated masses on a central shaft. The smallest has a slightly larger opening so that it can come off the shaft, while the others are trapped in place. If the whole assembly is dropped from 50cm or so about the table, the smallest ball on the end will fly off with considerable velocity, potentially rising to significantly greater than the initial height.

    Please be careful not to lose the small ball, and do not launch it into the audience or at anything else breakable.

    Engagement Suggestion
    • When presenting this device, describe it clearly, then encourage students to predict what will happen when you drop it.
    • Afterwards, have them discuss the results.
    Background

    The total energy of the system, of course, cannot increase beyond what it gains from the potential energy of the height from which it is dropped. But the elastic collisions of each ball with a successively smaller and less massive one transfer significant kinetic energy. With the smaller mass of the final ball, it can have a higher velocity than the collection as a whole did.

    C7

  • I7-23: Magnetic Track and Superconductor

    I7-23
    To illustrate levitation of a superconductor and magnetic pinning
    A chilled superconducting puck is levitated above a magnetic track. Despite the curve and slope of the track, the puck will remain above the track as it moves.

    This is an illustration of the diamagnetic and magnetic pinning effects of a superconducting material. When setting up, be sure to chill the puck in the position you want it above the track for maximum efficiency.

    The University of Cambridge has made available a helpful video lecture on magnetic pinning: https://ascg.msm.cam.ac.uk/lectures/fundamentals/pinning.php.

  • 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

  • J1-12: INDUCTION - ELECTROSCOPE

    J1-12
    Demonstrate charging by induction.
    A charged rod (black rubber in the photograph is negative) is held near the top plate of the electroscope, causing the electroscope to deflect. While the rod is in this position, the plate is touched by a grounded banana wire, and the electroscope returns to the uncharged position. When the charged rod is pulled away, the electroscope is charged positive, and deflects. This experiment can also be done using a positive glass rod to charge the electroscope negative by induction. The sign of the charge on the electroscope can be checked as follows: a rod with the same charge as the electroscope will cause further deflection of the electroscope when held close to the top plate, but a rod with charge opposite that of the electroscope will cause less deflection of the electroscope when brought close to the plate.
    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

  • J3-06 ELLIPSOIDAL CONDUCTOR

    J3-06
    Demonstrates that charge distribution on a conductor depends on the surface curvature
    The ellipsoidal conductor is charged, either positive or negative, using a charged rod from J1-01. Simultaneously touch proof planes to the larger and the smaller ends of the figure, and then to the corresponding electroscope. A few transfers show that there is more charge on the smaller end than on the larger end.
    J3b, J1b

  • 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

  • J3-14 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

  • J3-22: 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

  • 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

  • J4-12: 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

  • J4-22 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