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PHYS404

  • I1-12: THERMAL EXPANSION - BALL AND RING

    I1-12
    Demonstrate thermal expansion.
    When both ball and ring are at room temperature, the ball fits through the ring. If only the ball is heated, it expands so that it will not fit through the ring.
    I1, I0

  • I1-13 THERMAL EXPANSION - BIMETAL STRIP

    I1-13
    Demonstrates differential thermal expansion

    Two strips of different metals, invar steel and brass, are welded together to form a bimetal strip. Since each metal has a different coefficient of thermal expansion, heating the bimetal strip will result in the metals expanding at different rates, causing it to bend.

    When heating, always wear goggles and handle the flame with care, ensuring that it is not pointed near students or flammable materials. Use in a well ventilated classroom.

    Engagement Suggestion
    Ask your students: • Which metal will expand more when it is heated, and why?
    • What happens when it is cooled?
    • How could you make use of this to measure or control something?
    Background

    The amount a metal expands or contracts with temperature is governed by its coefficient of thermal expansion, a property which varies between different metals depending on their molecular structure. Invar steel is an alloy designed to have an exceptionally low coefficient, about one-tenth that of most steel, while brass has a higher coefficient than even ordinary steel. So the brass expands much more rapidly than the steel does when heated.

    Bimetallic strips like this are used in some types of thermometers and thermostatic controllers (including many older window thermometers and household thermostats). Check out demonstrations I1-17 and I1-18 for examples and to see how this works.
    I1, I0

  • I2-22 THERMODYNAMICS BY TOUCH

    I2-22
    Demonstrates that touching a material tells something about its conductivity, not necessarily its temperature
    Various materials, all at room temperature, are arranged on a cart, and students are invited to touch them. The materials in order of increasing conductivity, are: styrofoam, wood, plastic, slate, steel, aluminum, and copper.
    I2

  • I3-31: IDEAL GAS LAW - VOLUME OF ONE MOLE

    I3-31
    Demonstrate that one mole of gas occupies 22.4 liters at STP.
    Pour liquid nitrogen into the small beaker and let it boil down to about 35 ml. The density of liquid nitrogen is 0.808 g/ml, so one mole has a mass of 28 grams and occupies about 35 ml. Install the neck of the balloon over the beaker, and allow the liquid nitrogen to evaporate, filling the balloon. Determine the average circumference of the balloon and from that calculate the diameter. The approximate volume of one mole of nitrogen gas at atmospheric pressure is then V= 4 pi r3/3, which can be readily calculated. This determination is good to better than ten percent.
    I3, I0

  • I4-33: CRYOPHORUS

    I4-33
    Illustrate freezing caused by cooling by evaporation.
    Insert the lower end of the cryophorus into a liquid nitrogen bath, with the water in the sphere at the upper end. The liquid nitrogen will reduce the pressure inside the tube, causing evaporation of some of the water from the upper sphere. After sufficient cooling during the evaporation process, the remaining water in the upper sphere freezes.

    The photographs above show the water (left) before dipping the tube into LN and the ice (right) in the cryophorus tube.
    I4, I0

    i4-33ai4-33b

  • I5-11 ADIABATIC PROCESS - AIR PISTON WITH THERMISTOR

    I5-11
    Demonstrates adiabatic compression and expansion of air
    A thermister is enclosed in a small cylinder of air, the volume of which can be rapidly changed by moving a piston up and down. Pushing the piston down compresses the air, the air heats and the temperature increases, producing an increase in the resistance of the thermistor. Pulling the piston up expands the air adiabatically, the air cools and the temperature decreases, producing a decrease in the resistance of the thermistor. The thermistor is identical to those used in the thermometer probes of the old commercial digital thermometer.
    I5, I0

  • I5-21: HEATING AIR BY COMPRESSION

    I5-21
    Demonstrate heating air by compression.
    A few pumps of the tire pump into a mostly filled basketball warms the end of the pump noticeably. You can show that this is not due to friction by moving the pump handle back and forth in the same style with no load. You can simultaneously demonstrate cooling by expansion by observing that while the pump and the needle get rather warm, the air inside the ball actually cools.
    I5

  • I6-51 ENTROPY - SORTING MARBLES

    I6-51
    Demonstrates that increasing entropy requires less energy than decreasing entropy
    Shaking the system with the larger holes on the top causes the marbles to separate by size (yellow, green, pink, and blue). Simply inverting allows them to fall under the influence of gravity to their lowest level and mix. It apparently takes more energy to unmix the marbles than to mix them.
    I6

  • I6-52: ENTROPY - FOUR BALLS IN GAS DIFFUSION MODEL

    I6-52
    Demonstrate that an ordered state is statistically possible.

    Place two balls of each of two different colors in the diffusion apparatus. To start, either place all four one the same side of the apparatus; or place two of one color on one side of the apparatus, and two balls of another color on the other side. Start the machine going with the hole between sides open.
    Engagement Suggestions
    • Encourage students to notice that although statistically it is less probable, the arrangement of both orange balls on one side and both green balls on the other side will happen occasionally.
    • Ask: Is this as likely to happen using three balls of each color? With four?
    Background
    This is essentially showing the exception to the general principle of demonstration I6-21. With a small enough number of balls in the model, it is statistically possible to “reverse entropy” to a limited extent – that is, occasionally, the balls will randomly organize themselves so that they are once again sorted by color.
    FS1

  • I7-07: CLOSE-PACKED CRYSTALLITE

    I7-07
    Display the low index surfaces of face-centered cubic or hexagonal close-packed crystals
    Each plane is a two-dimensional hexagonal array. By stacking either abab or abcabc one obtains a hexagonal close-packed or face-centered cubic crystal, respectively. The face-centered cubic arrangement, for example, can expose (111),(100) and (110) surfaces simultaneously.
    I7