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PHYS260

  • 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

  • J4-03: PARALLEL PLATE CAPACITOR - SERIES CAPACITORS

    J4-03
    Demonstrate the effect of capacitors in series.
    The parallel plate capacitor is charged using a low-current DC power supply and separated as shown. A thin metal sheet is then inserted between the two capacitor plates, forming two capacitors in series. The voltage read by the electrometer remains virtually the same, indicating that the capacitance of the series capacitors is the same:

    C = C1 C2 / (C1 + C2),

    where either capacitance C is inversely proportional to the distance between the plates.
    J/K

    j4-03a

  • 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

  • J5-20 OERSTED EXPERIMENT- LARGE COIL AND COMPASS

    J5-20
    Demonstrates that magnetic fields are generated around current-carrying wires
    The compass is positioned within the coil. When current is run through the coil the compass lines up along the axis of the coil in the direction of the magnetic field.
    J5, PS1

  • K1-14 OSCILLOSCOPE CRT - DEFLECTION BY MAGNET

    K1-14
    Demonstrates the force on an electron beam by a magnetic field
    The beam of an oscilloscope CRT is viewed at the front on the fluorescent screen in the standard way. Holding a magnet near the CRT such that the magnetic field is perpendicular to the path of the electrons creates a magnetic force on the electron beam which deflects the beam, as can be seen on the fluorescent tube.
    K1

  • K4-02 MAGNETOELECTRIC GENERATOR WITH LAMP

    K4-02
    Demonstrates a small 110 VAC magnetoelectric generator
    A small magneto-electric generator is connected across a simple incandescent light bulb. Crank the handle to light the bulb.
    K4

  • K5-12 BATTERY AND CURRENT - WORKING MODEL

    K5-12
    Model of battery with circuit attached
    Though originally built as a toy, this device can be used as a model of an electric circuit attached to a battery. The "battery" raises the penguin "electrons" to a high potential. where they then progress through a "circuit" as they lose their potential. This model might indicate that a battery EMF provides energy which the carriers dissipate against resistance - the carriers do not speed up as they lose potential energy.
    K5

  • K5-31 OHM'S LAW

    K5-31
    Demonstrates relationship between current, voltage, and resistance

    This simple circuit consists of a variable voltage power supply and a socket that can hold one of three modular resistor units, with a ammeter measuring the current through the resistor and a voltmeter measuring the voltage across the resistor. The whole circuit is mounted on a transparent plate that can be placed on an overhead transparency projector to show the wiring and the meters.

    The voltage can be varied to show how the voltage and current change together in a linear relationship to the resistance. Both two 1,000 Ohm resistors and one 2,000 Ohm resistor modules are available; the two 1,000 Ohm modules can be placed in parallel if desired.

    It can be valuable to ask students to make predictions about how the results will change when you change the resistance, then afterwards have them discuss their predictions and compare them to the results.
    K5

  • K5-35: RESISTORS AT LN TEMPERATURE

    K5-35
    Illustrate materials with both positive and negative temperature coefficients of resistivity.
    Approximately equal copper and carbon resistors are mounted on long leads to a plastic mount, allowing them be inserted into a small liquid nitrogen bath. When cooled from room temperature to the temperature of liquid nitrogen, the resistance of the copper resistor decreases dramatically (first set of photos), while the resistance of the carbon resistor increases (second set of photos).
    K5, ME2, I0

  • K6-02: SERIES AND PARALLEL LIGHTS - FIVE BULBS

    K6-02
    Demonstrate combinations of series and parallel light bulbs.
    This demonstration consists of a series of 5 bulbs and a power supply that can be connected in various combinations. The top surface is illustrated with black lines showing the internal connections, which can be wired in various series/parallel combinations as desired by removing and replacing small shorting bars to complete the circuit. After wiring, the device is connected to 110 VAC power, the switch is turned on, and bulbs should light. Check for shorts!

    The photographs above show all of the lights in parallel (top) and all in series (bottom).
    K6

  • K7-14: RC CIRCUIT - 100 MICROSECOND TIME CONSTANT

    K7-14
    Demonstrate a reasonably fast RC circuit.
    Using a decade resistance box and a decade capacitor box a series RC circuit is produced. (1) It can be driven by a slow square wave (approximately 500Hz) and the voltage across the capacitor as the capacitor charges can be observed using the dual trace scope. (2) It can be driven by a sine wave (approximately 5kHz) and the phase shift between the voltage across the capacitor and the sine wave from the oscillator can be seen on the dual trace scope. See circuit above.

  • K8-03 LIGHT NANOSECOND

    K8-03
    Shows the distance light travels in one nanosecond
    This stick of wood is slightly less than 30cm. This length is the distance light travels in one billionth of a second
    K8

  • K8-13: RADIOWAVES - LECHER WIRE STANDING WAVES

    K8-13
    Illustrate standing electromagnetic waves in a high-impedance transmission line.
    Slide the fluorescent tube along the wires as shown. It will light up at the antinodal regions and remain dark at the nodal points of the standing wave along the transmission line.

  • K8-42: RADIOWAVES - ENERGY AND DIPOLE PATTERN

    K8-42
    Demonstrates transmission of energy in electromagnetic waves. Shows the radiation pattern of the dipole antenna

    This demonstration is centered on a simple radio transmitter with an antenna, which sends a signal to a handheld dipole antenna connected to a light bulb. The receiving antenna can be moved around in space, keeping the two antennas parallel, to observe the dipole radiation pattern. Rotating the receiving antenna to a vertical orientation shows that the radiowaves are polarized, as seen by the light going out.
    Background

    An antenna receives an induced current from the electromagnetic field of the passing wave. The dipole is a linearly polarized antenna, sensitive to signals oriented in a particular direction. In this experiment, we can see this dramatically, as changing the orientation of the antenna relative to the source produces a significant drop in signal strength, so that it is no longer receiving sufficient energy to light the bulb.

    Compare this effect to other wave and polarization demonstrations in sections G3 and M7.
    FS1