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PHYS132

  • G1-37: MASS ON SPRING WITH ULTRASONIC RANGER

    G1-37
    Plot graphs of position, velocity and acceleration for a mass oscillating on a spring.
    The ultrasonic range finder is used to plot graphs of position, velocity and acceleration for a mass oscillating vertically on a spring. Hanging masses with greater or lesser air resistance damping are available.
    Dr. Dan Russel of Penn State has developed some simulations of oscillating masses on springs that generate similar position graphs; compare the undamped and damped versions on his site.
    FS1, C2

  • G2-05: AIR TRACK - DRIVEN AND DAMPED OSCILLATIONS

    G2-05
    Illustrate the behavior of a driven and damped oscillator.
    A moveable glider, attached by stretched strings to a fixed glider at the left and an oscillator motor at the right, executes SHM when displaced and released. The oscillator can be driven by the variable frequency motor driver and damped by eddy currents by placing a magnet close to the base of the moving glider. The natural frequency of the glider can be changed by adding mass to the glider or by increasing the spring tension.

  • G2-09: FORCED HARMONIC MOTION WITH SONAR

    G2-09
    Plot a graph of forced damped harmonic motion near the resonant frequency.
    A computer and ultrasonic range finder is used to plot the motion of a large mass on a spring driven near its resonant frequency. With a large amount of damping, the result is a change in the amplitude of the oscillation, as shown in the photograph above.
    FS1, C2

    g2-09a

  • G3-01 SHIVE WAVE MACHINE - TRAVELING WAVES

    G3-01
    Demonstrates traveling waves

    Make sinusoidal waves by moving the spines at one end of the machine up and down sinusoidally, either with your hand or using the wave generator. Vary the amplitude and the frequency and observe the wavelength. You can show semi-quantitatively that the wave speed is approximately the same for all frequencies.
    Background
    The Shive wave machine illustrates transverse waves - the direction of displacement is perpendicular to the direction of transmission. This can be used as a model of many wave phenomena.
    FS0

  • G3-03: SHIVE WAVE MACHINE - REFLECTION OF PULSES

    G3-03
    Demonstrate reflection of pulses from fixed ends and free ends.

    A pulse generated at the left end (photograph at left) reflects off the right end. The reflecting end can either be fixed (clamped, center photograph) or free (right photograph).
    Engagement Suggestion
    • Encourage students to make a prediction before each combination as to whether the wave will reflect, and whether that reflection will be upright or inverted. • This can be combined with demonstration G3-05, showing that fixed and free end reflections are the extreme cases of partial reflections due to a change in impedance.
    Background
    Like any wave in a transmission medium, when the medium ends the energy in the wave has to go somewhere. The wave is reflected back from the end. With a free end, the wave reflects identically; with the end clamped, it reflects inverted.

    g3-03 g3-03a g3-03b

  • G3-21 TRANSVERSE WAVES ON A LONG SPRING

    G3-21
    Demonstrates traveling waves

    Clamp the spring to the lecture table and then step back. When you hold the other end with some tension and shake the end with various frequencies, you can illustrate transverse waves traveling along the spring.

    You can move your hand to generate a pulse or wave in the spring. Because of the clamp, the spring acts as a medium with one free end and one fixed end. By changing how far and how fast you move your hand, I can generate different amplitudes and frequencies. If you move my hand farther on each swing, you create a wave with a greater amplitude – the height of each peak is greater. If you move your hand up and down faster, you create a wave with a greater frequency – the number of peaks within a given length is greater.

    With practice, you can also find the natural frequency of the spring and set up standing waves.
    Engagement Suggestion
    • Ask students: “Now that we’ve seen some features of transverse waves, let’s try an experiment. I’m going to send a single upright pulse down the spring. What will happen when it reaches the fixed end? Will it stop entirely, bounce back in the same shape, or bounce back upside-down?”
    • “The pulse returns upside-down!”
    Background
    A transverse wave is one where the direction of oscillation is perpendicular to the direction of propagation. The up-and-down motion of the spring that forms each pulse is at a right angle to the forward movement of the wave. When a transverse pulse reflects off a fixed end, it returns inverted. If instead it had reflected off an open end, it would return upright. We can see this most easily with a single pulse, but this is true of a repeating waveform as well. We see mechanical transverse waves in springs, ropes, and other objects routinely. But another type of transverse wave surrounds us all the time – electromagnetic waves, like light, are transverse waves.
    G3

  • G3-24: SLINKY ON LECTURE TABLE - TRAVELING WAVES

    G3-24
    Show travelling waves.
    One end of the SLINKY is taped to the lecture table while theother end is free to move for creating waves. For best waves do not overextend the SLINKY.
    G3

  • G3-28 SUSPENDED SLINKY

    G3-28
    Shows longitudinal and transverse traveling waves & standing waves
    Transverse or longitudinal pulses can be created by appropriate motion of your hand at one end of the SLINKY. Using your hand you can also create transverse standing waves and discuss the overtone series. Gently vibrating one end of the spring (either by hand or using the motor) at the appropriate frequency creates longitudinal standing waves.
    FS1

  • H1-01 BELL IN VACUUM

    H1-01
    Demonstrates sound wave requirement for a medium

    An alarm-style electric bell is mounted inside a large glass bell jar, with external switches to control both the bell and the pump. This enables the instructor to compare the propagation of sound and light.

    Start the bell, then pump the air out of the jar. Air pressure in the jar is read by the large gauge. As the air is removed, the sound intensity decreases, ultimately to nearly zero. Turn off the vacuum pump when the jar is evacuated and crack the valve open, allowing air to re-enter the jar. As the pressure increases the sound of the bell comes back, but without the noise of the pump.

    Engagement Suggestion
    • Consider asking the students to make predictions before each step - how will removing the air change what they hear? What they see? What will happen as the air returns?
    • Compare this to videos the see of people working in the vacuum of space, in real life and in the movies. What do you see and hear in real life? How is this presented in fiction, and why?
    Background
    There are subtleties to this effect. The pump is not creating a true vacuum within the chamber. The vast majority of the air has been removed, reducing the environment’s ability to transmit sound; but the other (perhaps more important) effect in play is the difference in density between the interior of the chamber and the glass and the external atmosphere; this creates a major change in impedance, causing what little sound can be transmitted within the chamber to reflect back. Also, off course, the bell is not floating in free space, and some vibrations can always be transmitted through the supports and wires.

    For small groups, also consider H1-04, a more portable version of this demonstration.
    FS1

  • H1-02 SPEAKER AND CANDLE

    H1-02
    Demontrates longitudinal behavior of sound waves
    A lighted candle is placed directly in front of the center of a large loudspeaker, which is operating in the 10 Hertz range. The motion of the candle flame is longitudinal, following the motion of the air, illustrating the longitudinal nature of sound waves.

    With a bit of exploration, one can find resonances in the system that produce the most dramatic flame displacement. Consider having students make predictions about how different waveforms will make the flame respond differently
    OS5, ME2

  • H2-21 AUDIBLE YOUNG'S EXPERIMENT - GROUP LISTENING

    H2-21
    Demonstrates interference of sound waves with two coherent sources
    The oscillator-amplifier is set to approximately 3000 Hz, with identical signals being applied to both loudspeakers. Rotating the loudspeakers past the listeners allows them to observe the interference pattern by hearing the alternating maxima and minima in the intensity pattern.
    OS2

  • H2-32: SPEAKER WITH BAFFLE

    H2-32
    Demonstrates diffraction and interference of sound waves

    A small loudspeaker plays music with lots of bass, but the bass is not very loud. When the speaker is held up behind a hole the size of the speaker in a board about two feet square, the sound becomes much louder to the audience; this is particularly noticeable in the lower (bass) frequencies.
    Background
    A loudspeaker produces two distinct sound waves: one from the front and one from the back, which are out of phase with respect to each other. In the absence of the baffle, these sounds both diffract in all directions, and, because they are exactly out of phase they interfere destructively, especially the bass. The baffle forestalls the diffraction and thus reduces the magnitude of the interference. This effect is used in constructing speakers and their enclosures, to ensure that the maximum of output energy is passed to the listener. It can also be observed in nature, as some insects have been noted to use such surfaces to effectively amplify their calls in the wild (see references below).
    H2

  • H2-33: SPEAKER AND EXPONENTIAL HORN

    H2-33
    Demonstrate the effect of an exponential horn enclosure.
    A small loudspeaker is held up behind the opening of an exponential horn. The sound becomes much louder, especially in the bass. A horn enclosure has the effect of taking an extended source such as a loudspeaker and creating the best impedance match with the outside world, providing the most coherent plane wave. Compare this to H2-32, which uses the same speaker with a flat baffle. Invite students to speculate about what the effects the different shapes have.
    H2, OS5

  • H3-14 TWIRL-A-TUNE

    H3-14
    Demonstrates standing wave resonances in an open tube
    This popular toy is available in many stores and students may have seen it before, but this is an opportunity for them to explore how it works. To produce resonant frequencies of the tube, hold the tube by one end, keeping that end free for flow of air, and swing it around your head. Increasing the speed of the rotation raises the harmonic produced. Up to seven harmonics can be produced, illustrating the notes of the overtone series. The fundamental can only be produced by blowing gently into one end. SUGGESTIONS: Read Invited talk : Sounds Like Fun, presented by Paul Doherty of the Exploratorium at the 2004 meeting of the AAPT at Sacramento, CA, discussing how the twirl-a-tune works.
    H3

  • K2-40: MAGNETIC ACCELERATOR

    K2-40
    Demonstrate magnetic potential energy
    A slightly curved track holds a series of steel balls. One ball, superficially similar to the others, is a magnet. To use: Fill the track with nonmagnetic balls, and release a single ball from one upper end of the track. It rolls down and across the track until is collides with a stationary line of balls. As expected, the last ball in the line moves out with slightly less speed than the incoming ball. Now repeat the demonstration, replacing the first stationary ball in the line with the magnetic ball and the result is quite different. The attractive force of the magnet adds energy to the system, in a quite dramatic fashion.

    A similar effect can be seen with C7-19: Gaussian Gun
    K2

  • 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

  • L3-31 GIANT 160cm MIRROR - CONCAVE AND CONVEX

    L3-31
    Demonstrates images from concave and convex mirrors
    This five-foot diameter, 132cm (252-inch) radius of curvature parabolic mirror was originally designed as a solar collector on a satellite. Both convex and concave sides can be used with large classes or individually.

    Students can stand in front of the concave side at different distances to find the focal point. Invite students to predict the orientation of the image they see at different points, then try it out.
    FS0

  • L4-22: MIRAGE - LASER AND HOT WIRE

    L4-22
    Demonstrate how an optical mirage is created

    A laser beam is spread into a horizontal line by a cylindrical lens, and passes over a current-carrying wire aligned along the original laser beam. The hot wire causes the air to have a very strong decreasing temperature gradient a long the central section of the laser light line, so that section bends upward. The bent laser line is displayed on the wall or screen across a long distance (perhaps the width of the room), as seen below.

    Upward bending of blue light from the sky as it propagates along sun-heated sand in the desert causes blue light to appear to be coming from the ground, creating the classic illusion of a lake in the desert.
    L4, FS1, PS1

  • L5-11 LASER WATERFALL

    L5-11
    Demonstrates total internal reflection of a laser beam in a water jet

    A clear plastic tank with a plugged spout is elevated above a second, shallower tank. The upper tank is filled with water. A laser is aligned so that it passes through the upper tank and is centered on the spout.

    When the spout is unplugged, the water streams out into the lower tank. Several internal reflections of the laser beam should be visible in the outgoing stream of water, down to the point where it becomes too turbulent to see clearly.

    As the water level in the tank drops, the water flow becomes so slow that the stream bends too sharply and there is no internal reflection, and the laser beam ceases to follow the flow of water.

    Background:

    The laser here is illustrating internal reflection: depending on the index of refraction of the water and the angle the light hits it at, more light can be reflected back and forth within the stream of water than passes through it. At a certain point, it exhibits total internal reflection, where essentially all of the light is traveling along the stream rather than heading straight out the side.

    This demonstration can beneficially be used in combination with demonstrations of fibreoptic technology such as L5-13 or L5-23.
    OS2, LS1

  • L5-12 PLEXIGLASS SPIRAL

    L5-12
    Demonstrates total internal reflection
    Due to total internal reflection the light from the lamp remains mostly confined within the spiral plexiglass rod, and only exits at the end, where the angle between the surface and the incoming light exceeds the critical angle