Physics and Astronomy Demonstration Resources

          Demonstration Index                          

20a. Thermal expansion of nichrome as it is heated from room temperature to approximately 700 degrees C (wire looks orange) is demonstrated. One end of the wire is fixed, the other passes over a small pulley attached to which is a pointer. The wire is heated by passing a large electric current through it. A "guesstimate" of the coefficient of linear expansion for nichrome may be made.

20b. A gas thermometer is available for demonstrating the variations of volume with temperature. The device consists of a glass sphere attached to a fine capillary. The free end of the capillary sits in a bath of water dyed with sodium fluorescein and the change in the column of fluid noted as the bulb is heated. See file card for diagram.

20c. Cooled balloons in liquid nitrogen. Helium filled balloon shrinks to about 1/4 room temperature volume. The air filled balloon shrinks to near zero volume as the air inside the balloon liquifies. If removed from the liquid nitrogen, the balloons dramatically reinflate, especially the air filled. Use two colors for balloons.

20d. Glass thermometers using mercury or alcohol can be used to show the variation of volume of a liquid with temperature. Low visibility; can be used as a prop.

20e. The classic ball and ring demonstrations may be used to demonstrate the change in volume of a sphere or the change in area of an aperture as the temperature is changed. Two versions are available: One wherein the ball is larger than the ring and hence sits on it, unless the ring is heated, at which point the balls pass cleanly through the ring. In the second version, the ball is smaller than the ring. When it is heated, it is found that the ball will not pass through the ring.

20f. Electrical resistance of a heated iron wire wrapped around a ceramic form and the ends attached to a battery and galvanometer. The current flowing through the coil varies when a bunsen burner is played on the iron wire. Goes well with Experiment 27e.

20g. Thermal expansion of an iron bar set up vertically and firmly clamped at the top end. The lower end rests on a sheet of glass or a glass tube. Three bunsen burners are set up to heat the iron bar. When all the bunsen burners are lit, the bar expands, and after a short period of time, shatters the glass.

20h. Vibrating crystal model is available showing springs between "atoms". This may be used to demonstrate the vibration of atoms in a heated crystal or as a consequence of an inelastic collision.

20i. Bi-metallic strip shows the difference in expansion coefficients for metals. Demonstrated using the bi-metallic strip which consists of two bars of dissimilar metals welded together. When heated with a match or bunsen burner, the bar bends at the point of heating between 45 and 90 degrees.

20j. Convection in air may be demonstrated by using the candle convention apparatus which consists of a box with a glass front and two chimneys. Underneath one chimney, inside the box, is placed a lit candle. When a smoking piece of rope or brown paper is placed over the other chimney, smoke will be seen to be drawn into that chimney and will be connectively drawn through the box and out of the chimney above the candle. (See 20p)

20k. Thermal expansion of brass; an apparatus for quantitatively measuring the expansion coefficient of brass. The apparatus consists of a one-meter long brass tube through which steam is passed. One end of the tube is clamped, the other is attached to a roller pointer system which may be simply calibrated in terms of changes in length. The change in length as the apparatus goes from room temperature to 100 degrees C may be easily measured.

20l. Latent heats for water may be measured using a calorimeter. For latent heat of fusion, a calorimeter is arranged with an electrical heat supply which adds heat to the water of a calorimeter at a known constant rate. A quantity of ice at a known temperature is placed in the calorimeter and the temperature versus time curve of the water in the calorimeter is plotted. From this data it is possible to calculate the latent heat. The latent heat of vaporization of steam may be calculated from condensing a known mass of steam from the steam generator. When a sufficient mass of water has been condensed, the change in temperature and the change in mass are measured and from this data the latent heat calculated. Temperatures can be monitored and plotted using the computer.

20m. Leslie's cube which consists of a metallic cube four side faces of which are painted with black, smooth white, rough white, and polished metal is set up and fed with steam from the steam generator. The quantity of radiation emitted from each face is measured by a thermopile. Emissivity in far infra-red is not same as invisible, so some surprises occur.

20n. A thermopile radiometer is available for showing the radiation from a heated object. The device is sensitive enough to detect the presence of the human hand at approximately 1 m or a lump of dry ice two to three meters from the radiometer.

20o. A collapsible one gallon can is placed on a tripod with a small volume of water in it. The water is boiled for a period of time and the can quickly is sealed with a rubber stopper, placed on the lecture bench, and allowed to cool. As the cooling progresses, the steam inside the can condenses and the can collapses. This demonstration may be used as a demonstration of change of state or the pressure that the atmosphere exerts.

20p. Convection in water is vividly demonstrated by a glasstube bent to the shape of a rectangle and filled with water. A small quantity of dye or India ink is inserted through an opening in the top of the tube. When one vertical side of the tube is heated, the dye rapidly spreads throughout the tube due to convection in the fluid.

20q. Lighting a match with radiant energy can be demonstrated by using a book of matches at the focus of one parabolic reflector. An electric heater coil is placed at the focus of a second parabolic reflector placed approximately two meters from the first. After turning on the power to the coil, the matches will smoke after approximately one minute and will light after approximately two.

20r. Iron wire resistance; a coil of wire, preferably iron, is placed in series with a small light bulb and a small battery. The resistance of the coil of wire should be comparable with than of the bulb. When the coil of wire is placed into a dewar of liquid nitrogen, the bulb will be seen to glow much more brightly.

20s. Liquid nitrogen fun. Students are usually much amused by the classic demonstration of freezing flowers and crushing them, freezing bananas and shattering them, breaking a piece of rubber hose, racquet ball, etc. With liquid nitrogen being used for a demonstration such as 20c, 20r, 20t, these demonstrations can be performed with little additional difficulty.

20t. Boiling liquid nitrogen; a beaker is filled with liquid nitrogen and placed on a block of dry ice. The liquid nitrogen will be seen to boil rapidly. This is a nice demonstration of contrasts, not showing any particular physical principle. However, it is quite dramatic.

21. HEAT

21a. Heat conduction (1) is demonstrated by using a sheet of copper and a sheet of stainless steel which are bolted together and heated with a Bunsen burner at the junction. Matches are placed every 5 cm along each sheet. The rate at which heat is conducted from the center is demonstrated by the time at which the matches flare up. The first match on the copper side will flare at approximately 1 min.

21c. Heat conductivity (2) consists of a metal ring from which radiate six spokes of different metal. Attached to the end of each spoke with a lump of wax is a small metal object (a nut, washer, penny, ball bearing). When the center ring is heated by a bunsen burner, the wax holding the object melts at different times, depending upon the heat conductivity of the metal. The object will be heard to fall to the table. Success requires care that drafts don't blow the flame about; a transparent draft shield helps. Easier than the wax routine is the use of plastic fishline.

21c. Heat conductivity (3) consists of a cavity attached to which are five rods of different metals each coated with a thermochromic paint which changes from yellow to orange at 50 degrees C. Steam is passed from the steam generator through the cavity. The change in color is noted as it progresses up the various metal rods.

21d. Heat conduction (4): the great difference in conduction of heat for brass and wood is shown using a rod, half of which is brass, half of which is wood. Around the bar is wrapped a piece of tissue paper, the whole device being passed through a large bunsen burner flame. It will be found that the paper over the wood section of the bar rapidly chars whereas due to the high heat conduction of brass, the paper in that area will not char.

21e. Davy's safety lamp; the principle of the Davy safety lamp can be shown. A bunsen burner is placed beneath a fine copper mesh, flame being lit below the mesh. No amount of fanning, blowing, or poking will persuade the flame to light above the mesh. Thus, a flame enclosed by copper mesh will not ignite flammable gas outside of mesh, hence, a safety lamp in mines.

21f. Specific heats of four metals can be measured. Equal volumes of four different metals are heated to 100 degrees C in a pan of boiling water. They are then placed in turn in the glass calorimeter containing a known volume of water and a thermometer. From the masses of metal, volumes and the change in temperature of the water, the specific heat of the metals can be calculated.

21g. The mechanical equivalent of heat may be measured using a simple apparatus which consists of a long tube which is sealable at either end. A known quantity of lead show (in the order of two or three hundred grams) is placed in the tube and the tube turned end to end approximately 50 times. The shot is poured into a polystyrene cup and its change in temperature is noted. The increase in temperature in the lead shot and the height of fall of the lead shot are used to calculate the mechanical equivalent.

21h. Mechanical equivalent of heat, crank does work against friction and water changes temperature. See file card for details.

21i. Heat by wire bending. Students are handed short sections of iron wire approximately three inches long. That heat is equivalent to work may be demonstrated to the student's own satisfaction by having them bend the wire rapidly a number of times at one place. Upon touching the wire to the lips, it will be found that the wire has become quite warm.

22. THERMODYNAMICS

22a. A Rubber band as a heat engine: Each student is given a rubber band and asked to notice the temperature changes when the rubber band is held against the lips and stretched and contracted. Upon stretching the rubber band a distinct increase in temperature will be felt. If the rubber band has been allowed to return to room temperature by holding it stretched for a period of time, and then allowed to contract, it will be found that the rubber band becomes distinctly cool.

22b.  Rubber band heat engines: A rubber band is hung from a rod while holding up a weight.   If the rubber band is heated by a hair dryer, the rubber band will contract and lift the weight. Once the rubber band cools it relaxes back to its original length. The rod, rubber band, and weight system are shadow projected by a bright light to enhance the visibility for students.

22c. Sterling cycle engine is available for showing the principal of a cyclic engine. The sterling cycle consists of four parts: 1)heating at constant volume; 2) expansion at constant temperature; 3) cooling at constant volume; 4) contraction at constant temperature. This cycle differs from the carnot cycle in that the alternate quarter cycles are isovolumetric instead of adiabatic. The engine is small and quite inefficient but is capable of lifting a small weight. Heat may be supplied either from a propane torch or a small bunsen burner supplied with city gas. 

22d.  A transparent Sterling Engine model is available to use on an overhead projector. All parts are clearly visible.

22e.  An internal combustion model is available for demonstrating the principles of operation. The device simulates the four stroke engine with light bulbs simulating the firing of a cylinder.