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Safety Equipment: Tongs

  • I1-51: RUBBER AT LN TEMPERATURE

    I1-51
    Demonstrate how a normally elastic material at room temperature becomes rigid at very low temperatures.
    Dip a rubber sample into the liquid nitrogen with the tongs, then place it on a wooden "anvil" and hit it with a hammer to break it. Show the students in the audience how the material's property change with temperature.
    I0, I1

  • I2-12: RADIATION FROM COLD OBJECT

    I2-12
    Show radiation from a cold object
    If you put a hot object at the focus of one of the concave parabolic mirrors and a thermal probe at the focus of the other mirror, heat from the hot object will heat up the probe, yielding a temperature rise of the thermometer. (Compare the top and center pictures above.) If you put something very cold at the first focus, the temperature will drop. (Compare the top and bottom pictures above.) This demands a rather different explanation - blackbody radiation emitted by all objects - than the rather simple explanation given in the case of the hot object.

    This experiment demands the proper explanation in terms of blackbody radiation emitted by all objects, not just "hot" objects. The historical struggle of physicists to deal with this is documented in an interesting article by Hasok Chang, Lecturer in Philosophy of Science at University College, University of London, entitled Rumford and the Reflection of Radiant Cold: Historical Reflections and Metaphysical Reflexes, in Physics in Perspective Volume 4 Issue 2 (2002), pp 127-169.

    Note that this experiment uses materials from I5-51 and L3-16. If you want to use those demonstrations in the same class, be sure to discuss logistics with Lecture-Demonstration staff in advance.
    I2, I0, I5, L3

    I2-12A

  • I2-27: THERMAL EQUILIBRIUM BETWEEN ALUMINUM AND COPPER

    I2-27
    Show process of thermal equilibrium happening between touching aluminum and copper cylinders.
    Pieces of copper and aluminum are held together by a large C-clamp. Small holes are drilled into the pieces to a allow a digital thermometer probe to be inserted to measure the temperature of each block, showing that the blocks are initially the same temperature, at equilibrium. Remove the thermometer probes and put a flame under one block to create a temperature difference. Remove the flame, reinsert the probes, and watch as the blocks come to thermal equilibrium.
    I2, I0, tools

  • 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

  • I4-19: CONDENSATION OF STEAM - SODA CAN COLLAPSE

    I4-19
    Surprising demonstration using condensation of steam.
    A soda can with a small amount of water in the bottom is heated until the water boils, filling the can with steam. Very quickly the can is removed from the heater and inserted upside down into a container of cold water. The steam condenses so quickly that the can collapses, as seen in the photograph. This is quite a dramatic demonstration, and gets a good reaction from students.
    I4, I0, SU15

  • I4-31 ICE BOMB

    I4-31
    Demonstrates forces created by freezing water
    A pipe elbow with end caps is filled with water, sealed by tightening the ends, and dropped into a metal container of liquid nitrogen. Within about one minute the water freezes, expanding sufficiently to break the cast iron with a loud crack and a big cloud of vapor.
    I0, I4, SU5, OS6

  • I5-51: SPECIFIC HEAT - ALUMINUM AND COPPER

    I5-51
    Illustrate calorimitry and to determine experimentally the specific heats of aluminum and of copper.
    Boil the aluminum and copper blocks in a pan of water and place the metal blocks at 100 degrees C into equal amounts of water at room temperature in two styrofoam containers. Stir the water in the containers with the digital thermometer probe, measuring the temperature when equilibrium is reached. From these measurements the specific heats can be determined.

    Multiply the specific heat by the molar mass to find the molar specific heat. The values for both materials are nearly the same and equal to 3R=6(1/2)kT.
    I5, I0, ME1

  • 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

  • K2-61 THOMSON'S COIL

    K2-61
    Demonstrates a number of concepts in magnetic induction
    A large vertical induction coil with a fixed iron core rests on a power supply base. The coil can be activated by a momentary switch, and a variety of induction effects can be shown.

    Some demonstrations that can be performed with this apparatus: (1) JUMPING RINGS: Placing a ring over the extended primary coil core and switching it on causes the ring to jump. A smaller ring will jump higher. Cool the ring in liquid nitrogen to get a really great jump, but be careful about hitting the rear projection screen. Broken metal rings and wooden rings are unaffected. (2) RESISTIVE HEATING: Verify that there is resistive heating in the secondary ring by having a student hold it down until it gets too hot to touch! (3) A light bulb on a small coil lights up when the coil is moved over the extended core. (4) A secondary coil with small light bulb placed in a beaker on top of the secondary coil will remain lit when it is covered by water in the beaker.

    To understand the force on the jumping ring one must account for its self-inductance, which causes an extra phase lag of the induced current. The AC current in the coil produces an alternating magnetic field, which induces an alternating current in the ring. The ring thus experiences an alternating vertical magnetic force, due to the radial component of the magnetic field. (One can also think of this as a force between the two currents, repulsive when they are parallel and attractive when they are opposite.) Without self-inductance of the ring, the induced current would lag the magnetic field by a quarter cycle, and the time averaged vertical force would vanish. The self-inductance causes an additional phase lag, hence a repulsive average force. See Jeffery & Amiri, "The Phase Shift in the Jumping Ring," TPT 46, 250(2008), for a detailed explanation.

    An interesting historical note: This device is named for its inventor, electrical engineer Elihu Thomson, not for his better known contemporary J. J. Thomson, whose work with CRTs led to the discovery of the electron.

    Water, liquid nitrogen for cooling rings, and related accessories can be available upon request.

    Thanks to Prof. Ted Jacobson for assistance with this explanation.
    K2

  • 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