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Safety Equipment: Gloves

  • 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.

  • J7-14: 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

  • 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

  • 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

  • L3-16 FOCUSING OF HEAT WAVES BY MIRRORS

    L3-16
    Demonstrates that concave mirrors can focus heat waves
    Two parabolic concave mirrors are used to focus heat from a nichrome heater and light a match.
    L3, PW1

  • 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

  • N2-31: ABSORPTION SPECTRUM OF CHLOROPHYLL

    N2-31
    Demonstrate absorption spectrum of chlorophyll.

    A bright point source with condenser lens and iris is focused by a 20 cm focal length cylindrical convex lens onto a slit, which is in turn focused onto a distant screen by a 20 cm focal length spherical convex lens. A white light spectrum is obtained by inserting an equilateral prism just after the spherical lens. A chlorophyll solution, prepared by smushing up grass in a container of methanol, is placed in the beam just before the slit. The system now shows the absorption spectrum of chlorophyll.

    The color of chlorophyll is not a narrow band of green, but rather is achieved by removing the complementary color, magenta, through absorbing some of the red and much of the blue components. The absorption spectrum of chlorophyll is compared with the full spectrum of white light above.
    N2, OM1, LS1, FS1

    n2-31a n2-31b

  • 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)

  • P4-01: Radiation Monitor (Geiger Counter)

    P4-01
    Demonstrates radioactivity, the Radiation Monitor (Geiger Counter), and some differences between alpha, beta, and gamma radiation

    Radioactive mineral sources can be examined.

    Alpha particles have a range in air of about 2 or 3 cm; you must place the source close to the Radiation Monitor to observe the alphas. Inserting a piece of paper in the alpha beam stops them! Beta particles have a longer range in air, and are mostly unaffected by passing through a piece of paper. A thin lead sheet stops the betas, but some counting may remain due to the presence of a some gammas in the beta source. Gammas are unaffected by the paper or the thin lead sheet, but can be stopped by a lead brick
    SU19

  • P4-31: CLOUD CHAMBER - INDIVIDUAL VIEWING

    P4-31
    Observe alpha and beta particle paths with a cloud chamber.

    Sealed sources of alpha particles and beta particles are used with a small student cloud chamber to observe the paths of alphas and betas. The alpha paths (shown in the photograph) are very distinct and clear, whereas the beta paths are more diffuse. Cosmic ray products or gamma rays are also visible, but less distinct.

    The cloud chamber uses dry ice for cooling, and uses methanol to remove heat from the chamber and to provide the atmosphere of supersaturated alcohol vapor which condenses along the path of the ionizing particles to make the path visible.
    P4, I0

  • P4-32: CLOUD CHAMBER - TV

    P4-32
    Allow class observation of alpha and beta particle paths with a cloud chamber using TV.

    Sealed sources of alpha particles and beta particles are used with a small student cloud chamber to observe the paths of alphas and betas. The alpha paths are very distinct and clear, whereas the beta paths are more diffuse. Cosmic ray products or gamma rays are also visible, but less distinct. A TV camera views the "action," which is displayed on a monitor or on the rear projection system in the lecture halls (photograph at right).

    The cloud chamber uses dry ice for cooling, and uses alcohol to remove heat from the chamber and to provide the atmosphere of supersaturated alcohol vapor which condenses along the path of the ionizing particles to make the path visible.
    Nuclear Physics

    p4-32a