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PHYS272

  • 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

  • K5-44: NON-OHMIC DEVICE - LIGHT BULB

    K5-44
    Show the change in resistance of a light bulb with temperature.
    A 60 watt incandescent light bulb is connected to a switch so that it can be quickly disconnected from the 110 VAC power to an ohmmeter. The resistance of the 60 watt bulb in operation at a high temperature is R = V^2/P = 110^2/60 = 200 ohms. The resistance cold is about 18 ohms. Turn the bulb on, then switch it to the ohmmeter. The resistance starts high and drops quickly as the bulb cools.

  • K6-01 SERIES AND PARALLEL LIGHTS - TWO BULBS

    K6-01
    Demonstrates the effect of series and parallel connections of two identical light bulbs
    Two light bulbs can be wired in series or in parallel across 110 VAC circuit. Usually uses either 75 watt and 150 watt incandescent bulbs, or a pair of 40 watt bulbs. The voltage of the device can be reduced with a variac if desired.

    Important note: Turn off device before connecting or disconnecting wires! The bulbs can be wired either in series or parallel by swapping the wires, but this must not be done while powered.

    K6

  • K6-03 SERIES AND PARALLEL LIGHTS - BATTERY AND CLIP-ON WIRES

    K6-03
    Shows voltages and currents in series & parallel circuits
    Series and parallel combinations of light bulbs can be connected to the 7.5 volt battery source. Meters indicating current and voltage can be inserted in the circuit as required.

    Note that due to the aging of our large display galvanometers, this is better performed now with digital multimeters. A camera can be used to show them on the lecture hall screen if desired.
    K6, ME2

  • K6-11 CIRCUIT PARADOXES

    K6-11
    Series-parallel circuits to encourage dicussion about DC circuits
    Two circuits, with identical batteries and identical light bulbs, are connected with a switch through one branch of the circuit. (When using, be sure to check main power switch on underside.)
    K6

  • K6-12: SERIES/PARALLEL LIGHT CIRCUIT CONUNDRUM

    K6-12
    Test your ability to analyze series/parallel circuit.
    The circuit shown above uses three 1.5 volt batteries (a total of 4.5 volts) and five identical 1.5 volt light bulbs. In the photograph all of the switches are OFF, so none of the light bulbs is lit. The question is to rank the light bulbs in order of brightness when all of the switches are closed, putting all of the bulbs in the series/parallel circuit. The solution is shown above.
    K6

  • K6-23: HOT DOG COOKER - 110 VAC

    K6-23
    Illustrate the conversion of electrical energy into heat energy.
    A hot dog is mounted as shown in an overhead projection gizzit which skewers the hot dog between two nails connected to 110 VAC. The voltage applied to the hot dog and the current through the hot dog are displayed on the meters. The total energy can be found by plotting a graph of the current as a function of time and integrating. (Actually the current is pretty much constant so you can just take an average.) The initial and final temperatures are read by the digital thermometer, as seen in the photographs at the left and the right above. These pictures were taken using a fat-free vegetarian non-hot-dog. The cooking process is easier using a regular hot dog because the fat is an excellent electrical conductor. INSTRUCTOR MUST FURNISH ALL EDIBLE MATERIALS!!! Be sure to put the hot dog in the protective plastic shield provided so that grease will not splatter over the entire apparatus.

  • K7-02 RL CIRCUIT - L/R TIME CONSTANT

    K7-02
    Shows L/R time constant for a slow circuit
    A nine-volt battery is used to energize the LR circuit while the current through the LR system is observed on an oscilloscope. The system is then shorted and allowed to de-energize. This setup uses an approximately 6 kilohenry coil and about 12 kilohms series resistance to produce a time constant of about 1/2 second.

  • K7-03 INDUCTOR DELAYING A LAMP

    K7-03
    Demonstrates the timing of current in a switched inductor circuit
    An inductor and light bulb are connected across a battery with a switch. In parallel with this inductor and light bulb is a second identical light bulb. The separate light bulb will light immediately, but the light bulb in series with the inductor will be delayed in lighting until the current reaches a high enough level. The delay time is related to the L/R time constant of that leg of the circuit.
    K7, PS1

  • K7-12: RC CIRCUIT - RC TIME CONSTANT - PROJECTION METERS

    K7-12
    Measure an RC time constant and to observe the shape of the charging and discharging curves.
    An RC circuit with meters is mounted on an overhead projector projectual (the same setup as in K7-11). The voltage across the capacitor and the charging current are displayed on analog meters. Various combinations of resistance and capacitance can be plugged into the circuit. See circuit diagram above.
    K7

  • K7-15: CURRENT IN RC CIRCUIT?

    K7-15
    Demonstrate charging of a capacitor in a possibly counterintuitive way.

    A switch is closed to charge a 1 farad (yes, one FARAD) capacitor with a 3 volt battery (actually two 1.5 volt batteries in series). The capacitor has 1.5 volt light bulbs on each side of it in the circuit, as shown in the circuit drawing above.

    Consider the following series of questions:

    Q: What will happen when the battery is connected (switch turned to left position):

    (a) both bulbs will light and stay lit,

    (b) both bulbs will go on momentarily,

    (c) only one bulb will light and stay lit (if so, which one?),

    (d) only one bulb will go on momentarily (if so, which one?),

    (e) neither bulb will go on at all,

    (f) something else will happen (if so, what?).

    A: (b), Both bulbs will go on momentarily as the capacitor charges, then they will fade out. Click below for video

    Q: What will happen when the switch is opened (center switch position)?

    A: Nothing: the capacitor remains charged and no current flows.

    Q: What will happen when the switch is closed to the right, completing the circuit including the capacitor and the two light bulbs?

    A: The capacitor will discharge through the bulbs, turning them on momentarily while current is flowing, with the intensity decreasing as the current falls to zero. Click below for video.
    K7

  • K7-41: RC CIRCUIT - DIFFERENTIATION AND INTEGRATION

    K7-41
    Demonstrate differentiation and integration using RC circuits.
    A series RC circuit is used to obtain the derivative or the integral of a periodic electronic signal. For differentiation the time constant of the series RC circuit must be very small compared to the period of the wave. The derivative is sensed as the voltage across the resistor (current in the circuit). For integration the time constant of the series RC circuit must be very large compared to the period of the wave. The integral is sensed as the voltage across the capacitor. Waves from a signal generator are input into the circuit, including sine wave, triangular wave, sawtooth, and square wave. The appropriate circuits are shown above.

    Note that these circuit elements are very small, and hard to see in a classroom. A camera may be requested to display them on screen in the large lecture halls.
    K7, ME2, ME3

  • K7-61: TESLA COIL

    K7-61
    Demonstrate a tesla coil, including how magnetic induction and a resonant RLC circuit is used in the production of high-voltage high-frequency sparks.
    Our Tesla coil, circuit above, uses a 5000 volt transformer to charge a large oil capacitor. When the potential across the capacitor reaches the breakdown potential of the spark gap, breakdown across the gap occurs. The spark gap then becomes a conducting part of the RLC circuit, which resonates at a frequency of about 200 kilohertz. The large coil in the resonant circuit is the primary of the final transformer and the very fine coil is the secondary, producing about 200,000 volts at 200 kilohertz.
    Identify the components of the coil from the close-up of the figure at the right above.
    In the photograph the wires known as JACOB'S LADDER have been attached to the output terminals of the Tesla coil. A fluorescent light held by one end with the other end near the secondary coil will light by induction.
    DANGER: THE LOW VOLTAGE SECTIONS OF THIS DEVICE HAVE LETHAL CURRENTS.

  • K8-01 ELECTROMAGNETIC WAVE - MODEL

    K8-01
    Shows the relationship between the electric and magnetic field vectors in a plane-polarized traveling electromagnetic wave
    Red pegs represent the electric field vector and blue pegs represent the magnetic vector. The spatial relationship between these vectors and the direction of propagation can be seen. By moving the model along its axis the temporal aspect of the wave can be shown. This wave has a wavelength of 0.81 meters, and as an EM wave would have a frequency of 370MHz
    FS1

  • 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

  • K8-44: RADIOWAVES - COUPLING OF WAVES

    K8-44
    Illustrate inductive coupling using radio waves.
    A low-power 85MHz transmitter is coupled by an induction loop to a vertical transmitting antenna. A handheld dipole antenna with a lightbulb at the center serves as a receiver. Hold the receiving antenna near and parallel to the transmitting antenna. Change the coupling between the oscillator loop and the antenna loop by rotating the antenna loop. Coupling between the transmitter and the transmitting antenna is greatest when the light bulb between the two halves of the dipole receiving antenna glows brightly. When the loops are perpendicular there is little coupling and the bulb dims. When the loops are close and parallel the coupling is greater and the antenna bulb glows brightly.

  • 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

  • K8-52: MICROWAVE MAGNETRON

    K8-52
    Show students what the magnetron tube from a typical microwave oven looks like.
    Magnetron, as shown. Can be passed around to students. Handle with care, edges can be sharp.
    K8

  • P2-24: GIANT-LIGHT BULB

    P2-24
    Demonstrate color and intensity changes of blackbody radiation with temperature.
    The giant (1500-Watt) light bulb is connected to a transformer. With a low current, the filament is dim and orange. As the current is increased, the filament is seen to get brigher and whiter.
    P2

    p2-24ap2-24b