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Thermal Properties of Matter

  • I7-21: SUPERCONDUCTOR - MAGNET LEVITATION

    I7-21
    Demonstrate levitation of a magnet above a high-temperature superconductor
    A one-inch diameter superconducting disc is set on a conducting base in a bath of liquid nitrogen. A cubic samarium cobalt magnet levitates above the superconductor. Note that to show the Meissner effect you must place the magnet on the disc before cooling it down. When the superconductor passes through its transition temperature the magnet rises up by itself and levitates. For large groups, a camera can be provided.
    I7, I0

  • 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.

  • J2-17: ELECTRIC WIND

    J2-17
    Demonstrate the "electric wind" phenomenon.
    A lighted candle is positioned between a discharge point and a flat plate, which are in turn connecteed to a Van de Graaff generator as shown in the photograph. When the Van de Graaff is turned on, the "electric wind" blows the candle flame, as can be seen in the picture at the bottom.
    J2a

    j2-17a

  • 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

  • K3-05: DEMOUNTABLE TRANSFORMER - WELDER

    K3-05
    Show that very large currents can be produced in the secondary of a step-down transformer.
    A 500-turn primary coil operated at 140 VAC and 5-turn secondary coil form a transformer (using a demountable iron core). This is used to produce large secondary current. Holding two nails together tip-to-tip across the secondary produces over 100 amps in the secondary (stepped up from 4-5 amps in the primary), welding the two nails together.
    K3

  • K5-03: PIEZOELECTRIC IGNITOR

    K5-03
    Show a commercial use for piezoelectricity.
    Squeezing the handle stresses the crystal, creating a voltage sufficiently high that it creates a spark. These devices are used for starting fires with gas stoves, etc. This device is primarily for display, not for igniting things in the classroom.

  • K5-34: THERMAL COEFFICIENT OF RESISTANCE IN COPPER

    K5-34
    Show that the resistance of copper changes linearly with temperature.
    Measure the resistance of the copper coil at room temperature (295K), at the temperature of a dry ice and methanol mixture (195K), and at the temperature of liquid nitrogen (77K). Plot resistance versus temperature to demonstrate the linearity.
    K5, I0, ME2

  • 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

  • K5-36: RESISTORS AT LN TEMPERATURE - LIGHT BULB INDICATOR

    K5-36
    Demonstrate materials with both positive and negative temperature coefficients of resistance.
    Copper and carbon resistors are mounted on plastic tubes so that they can be inserted into liquid nitrogen. When the copper resistor is wired in series with a light bulb across 12 VDC, the bulb becomes brighter when the resistor is cooled to the temperature of liquid nitrogen, indicating a positive temperature coefficient of resistance for copper (first set of photographs). When the carbon resistor is wired in series with the light bulb across 12 VDC, the bulb becomes dimmer when the resistor is cooled to the temperature of liquid nitrogen, indicating a negative temperature coefficient of resistance for carbon (second set of photographs).
    K5, 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.

  • K6-21: HEATING IN CURRENT-CARRYING WIRE

    K6-21
    Show the conversion of electrical energy into heat.
    Push to attach 110 VAC to wire, heating the wire and causing it to become longer and sag. The marker hanging in the center of the wire indicates the sag.

  • K6-22: ENERGY CONVERSION - IMMERSION HEATER

    K6-22
    Demonstrate quantitatively the conversion of electrical energy into heat.
    This 300-watt immersion heater is used to heat approximately 300 ml of water in a borosilicate beaker. Measure the initial water temperature with a digital thermometer, allow it to heat for a fixed time, then measure the final temperature. Compare the temperature change calculated for the energy conversion (as per Q=mcT where ! is the energy transferredm m is the mass of water, c is the specific heat, and T is the change in temperature) to that measured, and invite students to talk about the meaning of the difference (heat loss through the sides of the beaker, etc.).

    Note that the heater will (obviously) get hot! Do not allow it to burn your hand or the power cord.
    K6, I0

  • L1-03: LIGHT BULB WITHOUT VACUUM

    L1-03
    Show what happens to a lighted filament in the presence of air.
    Turn on the light bulb so that it burns like usual. Gently position the drill against the bulb and turn it on; it drills through the glass in a few seconds. When air (oxygen) enters the bulb it rapidly burns up with a large vapor cloud.

  • L1-05: PERSISTENCE OF A FILAMENT

    L1-05
    Demonstrate that high-frequency AC looks like DC.
    A sealed beam car headlamp is run by an oscillator and audio amplifier. Below about 20 Hz the light flickers, but above 20 Hz it appears continuous. This persistence is caused partly by your eye and partly by the heating of the filament remaining relatively constant over the period of the applied AC voltage.

  • L3-18: FOCUSING OF HEAT WAVES - OVERHEAD PROJECTOR

    L3-18
    Illustrate focusing of heat in a very dramatic way.

    This demonstration uses one of the old overhead transparency projectors that focuses the light by a large parabolic mirror under the platform (rather than a Fresnel lens on the platform as in newer models), as seen in the images above. The heat filter and the mirror system above the projector have both been removed. There is sufficient heat focused about two feet above the projector to burn a piece of black paper in a few seconds. In a dark room, the focal point can be clearly seen as the smoke from the paper scatters the light.

    Engagement Suggestions

    Invite students to predict what would happen if you used white paper rather than black.

    • • Would it still burn?
    • • Would it take more or less time to ignite?
    Background

    This demonstration illustrates two important points. It clearly shows that light can be focused to a point by a curved reflector. It is also an illustration of infrared radiation, and the connection between light and heat. When appropriate to the course, consider combining this with a discussion of the wavelengths of the electromagnetic spectrum, and the relationships of energy, heat, and temperature.
    FS1

    l3-18a