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Safety Equipment: Goggles

  • 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

  • I4-51: SUBLIMATION OF DRY ICE - PROJECTION

    I4-51
    Demonstrate sublimation of carbon dioxide (dry ice) from a solid into a gas.
    Place a chunk of dry ice on the plastic sheet, on an overhead projector if desired. As the dry ice evaporates (evaporation sublimation) it becomes smaller but leaves no residue.
    I4, I0

  • I4-52: CARBON DIOXIDE BALLOON ON LIQUID NITROGEN

    I4-52
    Demonstrate condensation sublimation.
    A balloon filled with carbon dioxide gas is held on top of a liquid nitrogen bath. The volume of the balloon decreases for two reasons: (1) the volume of the gas shrinks according to Charles' law, and (2) the boiling point of carbon dioxide is well above that of nitrogen, so the carbon dioxide condenses, forming dry ice powder. The small granules of dry ice, which can be easily seen in the deflated balloon, disappear as the balloon warms up and inflates once again.

    i4-52a

  • I5-02: TRANSFORMATION OF MECHANICAL ENERGY INTO HEAT

    I5-02
    Demonstrate transformation of mechanical energy into heat.
    Use an electric drill to spin a wooden dowel rod in a hole on a large wooden beam. Shortly the contact point begins to smoke, indicating generation of heat due to friction.
    I3,I5

    i5-02a

  • I5-15: ADIABATIC EXPANSION OF CARBON DIOXIDE

    I5-15
    Illustrate adiabatic cooling by producing dry ice
    Carbon dioxide, leaked slowly out of the fire extinguisher onto a black felt cloth, produces dry ice, which can be easily seen. Adiabatic expansion and cooling occur when the CO2 gas comes out of the nozzle under high pressure and expands in the atmosphere. Enough is produced to pass the cloth around the class so that students can feel that it is actually cold. This experiment is a bit more complicated than simple adiabatic expansion. The carbon dioxide actually exists in the fire extinguisher as a liquid, so that much of the cooling is due to the evaporation of the liquid CO2 before it is ejected from the nozzle.
    FS1

  • 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

  • I5-41: ENDOTHERMIC REACTION - ENTROPY

    I5-41
    Aid a discussion of entropy.
    31.5 grams of barium hydroxide and 15.2 grams of ammonium thiocyanate, both solid powders initially at room temperature, are mixed. As they are stirred using the digital thermometer probe a chemical reaction occurs, producing water with barium cyanate and ammonium, both of which are soluble in the water. The solution becomes very cold, and can freeze a wettened wooden block to the bottom of the beaker.

    This experiment can be described in terms of entropy using two approaches: (1) As the mixture cools, it must become a liquid, increasing its disorder so that entropy will increase, or (2) The tendency toward disorder drives the reaction, creating the liquid reaction product.

    Note: PLEASE CALL THE LECTURE DEMONSTRATION GROUP AT 405-5995 NOT LATER THAN THE MORNING BEFORE YOUR REQUEST SO THAT WE HAVE THE TIME TO PREPARE THE NEEDED CHEMICALS.

  • I6-02: NITROGEN DIAMETER AND MEAN FREE PATH

    I6-02
    Experimentally determine the diameter of the nitrogen molecule and to determine the order of magnitude of the mean free path of nitrogen gas molecules at STP.

    Using the pan balance pour 700 cm3 of liquid nitrogen and demonstrate that it has a mass of about 560 grams. The mass of the dewar is about 421 grams. For liquid nitrogen the volume per molecule can then be determined to be

    Vol/Mol=700 cm3/[(560g)/(28g/mole)(1mole/6.0x1023molecules)]=5.8x10-23cm3.

    Assume molecule is a cube, so d = 3.9x10-8 cm.

    Volume per molecule @ STP = 22.4x103 cm3 / 6.0 x 1023 = 3.7x10-20 cm3

    Mean free path = V/d2 = 3.7x10-20 cm3 / (3.9x10-8 cm)2 = 2x10-5 cm.
    I6, I0, ME1

    i6-02a

  • I6-22: IODINE DIFFUSION TUBES

    I6-22
    Demonstrate diffusion.
    Two tubes are presented, both having a small amount of iodine crystals in the end. However, one contains air at a low pressure and the other contains air at near atmospheric pressure. When the iodine is heated, the difference in diffusion rate of the iodine through the two tubes is readily apparent.

  • 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

  • J4-11: POLAR AND NONPOLAR LIQUIDS

    J4-11
    Demonstrate that non-uniform electric fields produce a force on polar molecules.
    An electrophorus is used to charge an aluminum plate. A stream of carbon tetrachloride (CCl4), a non-polar molecule, is sprayed in front of the charged plate; the stream of carbon tetrachloride is unaffected by the electric field of the plate. A stream of water (H2O) sprayed in front of the charged aluminum plate deflects strongly, indicating that the centroids of the positive and the negative charges are not the same. The non-uniform electric field rotates the molecules and exerts a force on the dipole electric dipole of a non-polar molecule. Models of carbon tetrachloride and water are available to illustrate the polar nature of certain molecules.

    SAFETY NOTE: If you are hesitant to squirt around a volatile, carcinogenic liquid, a non-toxic alternative is light white paraffin oil, a squirt bottle of which is also provided.

  • J7-13 CURIE POINT OF NICKEL

    J7-13
    Shows the Curie point of nickel
    A Canadian nickel has the ferromagnetic element nickel as a major part of its composition, and is strongly attracted to a magnet. When heated above its Curie temperature by the gas torch, it loses its ferromagnetism and falls away from the magnet to the pedestal. After a few seconds it will again be pulled up to the magnet.
    J7, K1(magnet, bottom), I0

  • J7-14: CURIE POINT OF DYSPROSIUM

    J7-14
    Show the Curie point of dysprosium, a normally non-magnetic material.
    Dysprosium is non-magnetic at room temperature. When a dysprosium sample is cooled to the temperature of liquid nitrogen, it passes through its Curie point, becoming ferromagnetic. The dysprosium sample in the photograph has been cooled in liquid nitrogen and is strongly attracted to the magnet. As it warms, it passes the Curie point, becoming non-magnetic and falling into the liquid nitrogen bath, which cools it so that it becomes magnetic and is attracted to the magnet, where it warms up, etc....
    J7, K1 (magnet, bottom), 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

  • 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

  • M7-31 TYNDALL'S EXPERIMENT - COLLOIDAL SUNSET

    M7-31
    Colloidal sunset demonstration
    The collimated white light from the bright point source passes through the empty tank and hits a nearby screen. Chemicals previously prepared are then mixed in the tank: 2.5 ml sodium thiosulfate solution in 100 ml water, and 2.5 ml concentrated HCl 1:4 dilution in 650 ml water. When the chemicals mix they begin to form a suspension of sulfur particles which act as scattering centers for the light, especially blue light at first. This leaves the light on the screen with a yellowish tint. As time passes the sulfur particles grow larger and scatter more light and light of a longer wavelength, changing the light on the screen to a bright red. Ultimately most light is scattered, leaving no light on the screen.
    M7, LS1, OM1

  • P3-66: FLUORESENCE AT LN TEMPERATURE

    p3-66
    Demonstrate fluorescence of a normal material at LN temperature.
    The material does not fluoresce at room temperature. When cooled to the temperature of liquid nitrogen it will fluoresce when illuminated with ultraviolet light. The figures above show the material (a) at room temperature, (b) at LN temperature with room lights on, and (c) at LN temperature with room lights off.
    P3, I0

    p3-66ap3-66bp3-66c

                               (a)                                                       (b)                                                         (c)