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Safety Equipment: Goggles

  • I1-63: HYDROGEN EXPLOSION

    I1-63
    Produce a hydrogen explosion

    A balloon filled with hydrogen is tethered about six feet above head level. The burning match on a stick is positioned under the balloon, creating the hydrogen explosion.
    Engagement Suggestion
    • One option for presenting this would be to compare the behaviour of two different balloons, hydrogen and helium. You can tell students what is in each balloon and have them make a prediction about what each will do, or show the demonstration first and then have students analyze why the results were different.
    I1, I0, FS1

    I1-63B

  • I1-64: BURNING CANDLE - COMBUSTION PROCESS

    I1-63
    Demonstrate features of the burning process and to debunk myths about this supposedly well-known demonstration.

    A common pre-college experiment is to burn a candle inside of a bottle which has been turned upside down over a container of water. The water supposedly rises about one-fifth of the way up the bottle, indicating that the oxygen, about one-fifth of the air in the atmosphere, has been "used up" in the combustion process.

    The candle in our experiment is placed inside the sealed tube containing air above a colored water bath, and is then ignited by a hot wire (center photograph). The water level goes down initially, then returns to its original level just after the candle goes out. There is virtually NO CHANGE in the water level from before to after the experiment is performed (photograph at right).

    This is the CORRECT WAY to do this experiment. Two experimental errors are often made when performing this experiment: (1) if the candle is lit before the bottle is placed over it, the air is initially hot, and will pull the water up the bottle as it cools, and (2) when the bottle is placed over the candle, the hot air from the candle flame expands, and some of it might escape out of the bottom opening of the bottle. Analysis of the chemistry of this experiment shows that the final products of combustion are actually more voluminous than the initial air, but other things happen to yield no net difference in the water level.
    I1

    i1-64a

    i1-64b

  • I2-01: CROOKES' RADIOMETER

    I2-01
    Stimulate discussion about radiative heat transfer and conservation of momentum with photons.
    A match or other source of light is brought near the radiometer, resulting in rotation of the vanes. The REAL reason has to do in a very important way with details regarding how molecules interact with each other. The explanation is not nearly as simple as the difference in the momentum of photons when they are absorbed or reflected, or even as simple as the heating effect on the black side, which absorbs more photons, compared with the white side, which reflects more. This appears to be one of those physics devices that is typically explained incorrectly, even in the literature from the supplier that accompanies the radiometer.
    I2

  • I2-07: THERMOPILE WITH DVM

    I2-07
    Observe infrared radiation.
    The output from a commercial thermopile is connected to a digital voltmeter where the voltage is proportional to the temperature observed: the hotter the object the higher the voltage. Use various sources: ice, boiling water, liquid nitrogen, the floor, people, etc. This is only qualitative; the system is not calibrated.
    N1, ME2, I2, PW1

  • I2-09 DEWAR - TRANSPARENT WITH LIQUID NITROGEN

    I2-09
    Demonstrates a dewar
    The dewar contains liquid nitrogen, which can be seen as a clear liquid. Various experiments using liquid nitrogen can also be performed
    I2, I0

  • 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

  • I2-21 THERMAL CONDUCTIVITY IN METALS

    I2-21
    Demonstrates thermal conductivity in various metals
    Heat from a gas burner at the center is conducted along rods of copper, aluminum, and brass. Wax blocks at the ends of the rods melt and drop off the rods due to the conduction of heat, in the following order: copper (3.98 Watts/cm deg C), aluminum (2.37 Watts/cm deg C), and brass (1.23 Watts/cm deg C).
    I2, I0

  • I2-24: THERMAL CONDUCTIVITY IN WATER

    I2-24
    Demonstrate that water is a poor conductor of heat.
    An immersion heater placed at the top of a dewar of water causes the water near the top of the dewar to boil. However, heat is not readily conducted through the water to the bottom, and the bottom remains at a much lower temperature even 15-20 minutes after the water on top begins to boil.

  • 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

  • I2-28: WATER BALLOON AND CANDLE

    I2-28
    To demonstrate the transfer of heat by water
    A balloon filled with water is held above a candle flame. Contrary to most students' expectations, the balloon does not burst. The water in the balloon conducts heat away from the rubber before it can melt.
    I0

  • I2-41: CONVECTION - POWDER IN WATER

    I2-41
    Illustrate convection.

    Heat one side of the tube, and the water will rise on that side by convection, carrying the powder, which makes the convection visible. To avoid overheating and destroying the apparatus, heat only for about ten seconds in a blast. Before beginning, rotate the entire apparatus so that the powder is uniformly distributed.

    A video camera may used to enlarge the action in the lecture halls.

    Background:

    The isolated heat source produces convection currents through the apparatus. Heated water rises up one side of the loop, drawing powder with it, while cooler water is drawn down the other side.
    I2

    i2-41a

  • I2-42: FALLING CANDLE

    I2-42
    Demonstrate how a flame burns in the absence of normal convection.
    A candle, attached to the lid of a one-gallon jug, is lit and the lid screwed onto the upside-down jug. Throw the upside-down jug into the air and catch it or hold the upside-down jug high and drop it and catch it as it falls. While it is falling, the system inside the jar is in a weightless environment, so convection currents cease. In normal burning, the hot air rises by convection, allowing cooler air containing more oxygen to continuously feed the fire. Without these convection currents the candle should immediately go out, BUT IT DOES NOT.
    I2

    A candle mounted on the lid of a gallon jug is lit, and the lid quickly affixed to the jug. In this configuration the candle will remain lit for over one minute before the oxygen in the jug is sufficiently used up by the combustion process and the flame is extinguished.

    Now suppose that the candle flame is lit and the lid again quickly affixed to the jug. However, the bottle is now dropped about six feet starting from the orientation shown in the photograph below.

    i2 42

    What will happen? In particular, by the time the jug falls six feet the candle flame will:

    • (a) burn more brightly.(b) remain at about the same brightness.
    • (c) burn less brightly.
    • (d) go out.

     

  • I2-45: CONVECTION - HIGH/LOW CANDLES IN CYLINDER

    I2-45
    Brainteaser regarding convection.

    Two candles, one at the level of the table and one raised approximately 30 cm, are lit and then covered by a tube about 50 cm high and 10 cm in diameter. The tube is sealed at the top by a dark plastic cover to prevent air from flowing into the tube as the experiment progresses.

    Engagement Suggestion:
    • Encourage students to predict which candle will go out first, and why.
    • As the demonstration will typically take 2-4 minutes, discuss other related matters and then check in on the demonstration from time to time; ask students if it is behaving as they expected.
    • When both candles have gone out, ask students to discuss what they saw.
    Background:

    As the candles burn, the hot gases composing the products of combustion will be less dense than the cooler original air, and will rise to the top of the tube. The upper candle will therefore be extinguished sooner than the lower one.
    I2

    ii2-45ai2-45bi2-45ci2-45d

     

     

    Two candles, shown in the photograph at the left below, are lit and then covered by a plastic tube (sealed at the top), as seen in the photograph at the right below. In the apparatus as pictured the tube is about 50 cm tall and 10 cm in diameter, and the upper candle is about 30 cm from the bottom.

     

    i2 45 i2 45a

     

    After some period of time, as the oxygen in the tube is consumed by the candle flames, the candles will both cease to burn. The question involves the order in which the candles will go out.

    Which of the following statements is true?

     

     

    • (a) The top candle will go out first, then the bottom candle.
    • (b) The bottom candle will go out first, then the top candle.
    • (c) Both candles will go out at the same time.

     

  • I3-16: COLLAPSE OF CAN - LARGE PUMP

    I3-16
    Demonstrate the forces created by atmospheric air pressure.
    Start the mechanical vacuum pump, then place a soda can firmly on the top gasket around the pump opening. In a couple of seconds enough air is pumped out of the can so that the can collapses with a bang, jumping off the pump.
    FS1, SU14

    i3-16ai3-16b

  • 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

  • I3-33 HELIUM BALLOON ON LIQUID NITROGEN

    I3-33
    Demonstrates how a gas contracts when cooled
    A helium balloon which is cooled by resting on a liquid nitrogen bath becomes becomes more dense -- by about a factor of 4. When the balloon is removed from the liquid nitrogen it warms up, expands, and floats away, unless it is tethered
    I0, FS1

    I3-33A

  • I4-13: CHANGE OF STATE OF LN - POPPING CAN LID

    I4-13
    Show the increase in volume which accompanies the transition from liquid to gaseous nitrogen.
    Pour a small amount of liquid nitrogen into a can (typically under 10ml) and install the plastic lid. The liquid nitrogen heats up, changes to a gas, and forces the lid open.
    I4

  • I4-14: CHANGE OF STATE WITH BANG

    I4-14
    Demonstrate that the volume of a gas is much greater than the volume of the same amount of liquid.
    Fill the small flask with liquid nitrogen and place the balloon over the top. As the liquid nitrogen turns to gas its volume increases, ultimately bursting the balloon. This is a change of state with a bang, hee, hee, har, har.
    I4, I0

  • I4-17: AIR BALLOON ON LIQUID NITROGEN

    I4-17
    Demonstrate dramatically that the volume of vapor is greater than the volume of the same amount of liquid.
    An air balloon is held on top of a liquid nitrogen bath. The volume of the air balloon decreases for two reasons: first, the volume of the gas shrinks according to Charles' law, and second, some of the air changes to liquid and shrinks considerably. Liquid nitrogen will readily cause oxygen to liquify, and even liquify some of the nitrogen in the balloon.
    I0

    i4-17a

  • 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