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  • H5-13: WAVETEKS AND AUDIOCART - MASKING

    H5-13
    Demonstrate masking.
    The first oscillator, the "masking" tone, is set to a 500 Hz sine wave at medium intensity. The second is to be the "masked" tone, which will be varied in frequency and in intensity. The second tone is easily masked when its frequency is higher and its amplitude lower than the masking tone. Masking occurs very readily when the second tone is up one octave, twice the frequency of the masking tone. Frequencies below the masking tone are not easily masked, even at relatively low amplitudes.

    Masking phenomena are significant in understanding the process of hearing. When analyzing a complex sound, it is notable that masked components can be altered or removed without substantially changing the experience of hearing.

  • H5-15: EFFECT OF HARMONIC CONTENT ON TONE QUALITY

    H5-15
    Illustrate Ohm's Law of Hearing, and to hear the sounds of complex waves produced by the Fourier Synthesizer.
    A Fourier Synthesizer including 12 harmonics with independently adjustable amplitudes and phases is connected to an oscilloscope and loudspeaker. Several relevant demonstrations can be performed using this setup: (1) Produce various wave shapes. Listen to the difference in sound as each harmonic is added while the wave is being synthesized. Compare the sounds of the different wave shapes. (2) Demonstrate that although the wave shape changes when the phase of any of the harmonics is changed, change of phase of harmonics has a negligible effect on the timbre or tone quality. Ohm's Law of Hearing states that the sound of a complex tone is to a great degree independent of the phases of the harmonics. (3) Remove the fundamental from a complex tone - best for the pulse train, which has large-amplitude harmonics. The frequency of the fundamental is still audible due to difference tones created by the non-linear mechanism of the ear. The frequency of a complex wave is due in large part to the combined effect of all of the harmonics, illustrating the "missing fundamental."(4) Demonstrate fundamental tracking by varying the frequency of the synthesizer with the fundamental missing. The ear follows the missing fundamental frequency.
    H5, ME2, ME3

  • H5-17: WAVETEKS AND AUDIO CART - QUALITY BEATS

    H5-17
    Demonstrate second order or quality beats.
    One oscillator is set at about 200-500 Hz sine wave, and the other set to the second harmonic (an octave higher) but with about half the amplitude of the fundamental. If the octave is slightly mistuned, the phase of the second harmonic will be continuously changing with respect to that of the fundamental. The slight change in tone quality or timbre is known as "quality beats" or "second order beats." Inasmuch as quality beats are significant, this experiment provides a counterexample to the general statement of Ohm's Law of Hearing.

  • H5-19: SUM AND DIFFERENCE TONES

    H5-19
    Quantitatively demonstrate sum and difference tones.
    Set the two oscillators to equal amplitudes with frequencies of 500Hz and 700 Hz, so that the combination tones are not masked by being related harmonically. When the volume of the system is turned sufficiently high, several difference tones will immediately be heard: 200 Hz, 300 Hz, and 400 Hz. Move the frequency of one of the oscillators back and forth by a small amount to call attention to the difference tones. The extra oscillator and speaker can be set to the difference frequency so that it can be identified by the observer. Sum tones also occur, the best example being at 1200 Hz, but it cannot be heard due to masking by the two louder original tones. However, tuning the extra oscillator to a frequency of 1200 Hz at a low a amplitude will allow it to beat with the sum tone, thus indicating that the sum tone is actually there!
    FS1, ME3

  • H5-31: DIPLACUSIS AND BINAURAL BEATS

    H5-31
    Demonstrate individually the phenomena of binaural beats and diplacusis.
    Two sine wave oscillators present their signals separately to the two ears using stereophones through the Diplacusis and Binaural Beat Demonstrator. Binaural beats occur in the brain when the frequencies of the two waves are very close, but the two waves do not physically mix to create first order or monaural beats. The amplitude of the two waves is kept small enough to avoid bone conduction. A subject is asked to match the pitch of the two oscillators under these circumstances, which is very difficult even for most trained musicians. Diplacusis refers to the inability to match pitches when the two tones are presented to separate ears. The two tones can be combined by flipping a switch on the Demonstrator, and the sum wave can be displayed on the oscilloscope. Several listeners can observe the proceedings through individual stereophone jacks.
    H5, ME2, ME3

  • H6-01: FOURIER ANALYSIS OF VOICE

    H6-01
    Determine the Fourier spectrum of various steady-state spoken and sung vocal (vowel) sounds.
    An amplified microphone is fed into a digitizing oscilloscope with an FFT function. The wave shape and spectrum are displayed on screen.

    Consider inviting students with different voices up to try it out, and show how the vocal formants appear at different intonations. Compare the underlying structure to show how speech remains understandable even as formants shift.
    H6, ME2, ME3

  • I1-14: THERMAL EXPANSION OF ALUMINUM - OPTICAL LEVER

    I1-14
    Demonstrate thermal expansion in a complicated way.
    A small mirror with an iron lever attached to it rests on one end of an aluminum tube. The other edge of the lever rests on the pole of a magnet. When the aluminum tube is heated with a burner the mirror is deflected. To measure this deflection a laser beam is reflected off the mirror onto a scale as shown in the picture. When the tube is heated the laser spot is deflected about 50 cm when the distance between the mirror and the scale is about 2 m. The picture at the right is a detail of the mirror mount.
    I1, I0

    i1-14a

  • I1-15: THERMAL EXPANSION - PIN BREAKER

    I1-15
    Demonstrate thermal expansion in a dramatic way.
    A pin is inserted into a hole in a long steel rod, one end of which is fixed on the apparatus. The pin sticks out of the hole and rests against a fixed plate at the right side of the device, under the shield. When the rod is heated over period of several minutes, it expands such that the pin pushes against the plate, as seen in the photograph at the right, until the pin snaps. This is a fairly dramatic demonstration which illustrates the magnitude of the forces which can build up during thermal expansion.
    I1, I0

    i1-15a

  • I1-17: THERMOSTAT - MODEL

    I1-17
    Model of use of a bimetal strip in a thermostat.
    A bimetallic strip is set up to complete a circuit and turn on a bulb, as a model of how thermostats move with changing temperature to control furnaces or air conditioners. Heat the bimetal strip so that it curves toward the wire. When it touches the wire it completes the circuit, lighting the bulb. This is similar to the mechanism in a real bi-metal strip thermostat to turn on and off the power to the appliance.
    I1, I0, K6

    i1-17a

  • I1-22: WATER DENSITY VS TEMPERATURE

    I1-22
    Demonstrate the change in the density of water with temperature.

    A calibrated thin spherical metal shell with air and shot inside sinks in water at approximately 115-120 degrees F. The water is then cooled by a fan, whereupon the sphere rises to the top of the water when a temperature of about 100-110 degrees F is reached (this cooling can take up to 15 minutes depending on room temperature and humidity).

    The water can be stirred continually to keep the temperature uniform using the digital thermometer probe, which simultaneously reads the temperature, which is displayed on a large scale. If the sphere starts out floating and is sunk by heating the water, the demonstration requires more time due to surface tension.
    I0, I1

  • I1-41: THERMOELECTRIC MAGNET

    I1-41
    Demonstrate production and use of thermoelectric current.
    One junction of the thermocouple is kept at the temperature of ice, and the other heated by a burner, thus generating a large thermoelectric current. The current forms a single loop through the two sections of an electromagnet. The bottom section is a 5 kG mass, which can be supported by the magnetic field created by the thermoelectric current when the device is lifted by the hook on the top section after about 2 minutes of heating.

  • I1-61: DUST EXPLOSION

    I1-61
    Produce a dust explosion.
    A rounded tablespoon of lycopodium powder placed in the funnel is blown upward by blowing into the end of the rubber tube, which can be stretched out. When the cloud of powder reaches a burning candle flame, on the top mount, it ignites readily to create a dust explosion. This is a very dramatic effect.
    I1, I0, C2, FS2

    i1-61ai1-61b

  • I2-25: THERMAL CONDUCTIVITY IN BUILDING MATERIALS

    I2-25
    Determine thee thermal conductivity of some commonly used building materials.
    A slab of material 1/2 inch thick is placed between two 1-liter plastic bags, each containing 2.2 lbs of water. The thin plastic bag allows good conductivity between the water and the surface area of the insulating slab. One bag contains water at room temperature and the other contains water initially at a temperature of 180-190 degrees Fahrenheit. The outer sides of the water bags and the insulating slab are surrounded by a styrofoam box at least three inches thick. Measurements of the temperature of the water on each side are made at regular time intervals and the average temperature difference is determined over some total time. The conductivity is then calculated in units of BTU/inch second degree Fahrenheit.

    Note: This measurement is not very precise. Comparisons between different materials can, however, be easily made. Check bags for leaks, particularly if very hot water is used.

  • 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

  • I2-44: CONVECTION - CANDLE IN CYLINDER

    I2-44
    Demonstrate the mechanism of convection.
    A lighted candle lowered into the graduated cylinder goes out quickly because the buildup of gaseous products of combustion at the bottom of the tube prevents it from getting oxygen. Lowering the smaller tube into the larger graduated cylinder just above the candle flame separates the rising hot air from the falling cold air, allowing convection currents to feed oxygen to the candle flame.
    I2

  • 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.

     

  • I3-13: INVERTED GLASS OF WATER

    I3-13
    Show one result of atmospheric pressure.
    Fill a glass or jar with water and lay a stiff, flat index card on the top. Holding the card and glass together, turn them upside down and release the card. Tilt the glass slightly. Atmospheric pressure holds the card onto the opening of the glass.
    I3

  • I3-18: VACUUM BAZOOKA

    I3-18
    Illustrate one effect of atmospheric pressure and force.
    A tennis ball is positioned near one end of an evacuated tube. When the plate sealing that end of the tube is rapidly knocked off, air at atmospheric pressure enters the tube. The ball is propelled by the force arising from the atmospheric pressure of air to create a bazooka effect along with a loud noise.
    I3, I0

    i3-18a

  • I3-19: LIFTING USING ATMOSPHERIC PRESSURE

    I3-19
    Dramatically demonstrate an effect of air pressure.
    A rubber cup with a molded handle is held in contact with some horizontal object like a wooden box (in photograph above) or a cart top. Pulling upward on the handle allows you to lift the object, due to the ability of atmospheric air pressure to hold the rubber sheet in contact with the surface.
    I3

    i3-19ai3 19

  • I3-35: SOLAR BAG

    I3-35
    To demonstrate how the density of a gas changes with temperature.
    This is a large bag that will float when the air inside is heated. On a sunny but cool day, unroll the solar bag outside in the shade and fill it with cool air. Tie off the open end. Tie the string to the tied-off end, and move the bag into direct sunlight. The solar bag will soon float as the air inside heats up and expands. Obviously, this demonstration is primarily suited to outreach programs held out-of-doors, not to classroom use.
    I3