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PiP Oct 2014

  • H3-17 FLAME TUBE

    H3-17
    Demonstrates standing waves in a tube
    A loudspeaker in one end of a four-inch diameter galvanized iron tube creates standing waves in propane gas in the tube. The gas emerges out of a series of small holes in the top of the tube, forming a long line of flames when lit. Any sound resonant with the length of the tube can create standing waves in the gas which are readily visible as a pattern in the height of the flames. Both rhythm and frequency response can be seen nicely in music. An oscillator and a cassette deck are provided with the demonstration to be used as simple sources for the loudspeaker. Or, a voice or other music or audio can introduced using a microphone and amplifier or external input jacks, available upon request.
    FS1

  • I7-21: SUPERCONDUCTOR - MAGNET LEVITATION

    I7-21
    Demonstrate levitation of a magnet above a high-temperature superconductor
    A one-inch diameter superconducting disc is set on a conducting base in a bath of liquid nitrogen. A cubic samarium cobalt magnet levitates above the superconductor. Note that to show the Meissner effect you must place the magnet on the disc before cooling it down. When the superconductor passes through its transition temperature the magnet rises up by itself and levitates. For large groups, a camera can be provided.
    I7, I0

  • J1-06: FUN-FLY-STICK

    J1-06
    Demonstrates electrostatic fundamentals
    This is a battery operated static electricity generator that allows you to float tinsel shapes above the electrically charged stick. Since like charges repel each other, the negatively charged tinsel floats above the negatively charged stick.
    J1b

  • J1-24 ELECTROSTATIC HAIR RAISING

    J1-24
    Demonstrates electrostatic repulsion
    While standing on a large styrofoam insulating block, touch your hands to the top of the Van de Graaff dome, then have someone turn it on. The fact that your hair stands on end is a result of the repulsion between charges of the same sign that collect on your hair.
    J1a, OS2

  • J1-26 VAN DE GRAAFF - REPULSION OF PIE PANS

    J1-26
    Demonstrates electrostatic repulsion

    A group of aluminum pie pans is placed on top of the Van de Graaff dome and the Van de Graaff is turned on. The pie pans are pushed off the top of the dome one at a time by the electrostatic repulsion. Use this as a way to argue that electrostatic forces might be stronger than gravitational forces.

    Engagement Suggestion:
    • Before turning the generator on, encourage students to predict what is going to happen. Challenge them to explain their hypotheses in terms of what they have learned about the behaviour of electrical charge.
    • Feel free to invite students to collect the scattered pans, but remind them not to get close to the Van de Graaff while it is turned on.
    J1a

  • J2-01: WIMSHURST MACHINE

    J2-01
    Generate high electrostatic potentials.
    Cranking the handle rotates the two plates in opposite directions, generating a large electrostatic potential. The Leyden jars can be charged to increase the intensity of the spark between the two balls on the arms mounted above the Leyden jars. This machine can also be used for other demonstrations requiring high potentials. This gizmo may go up as high as 500,000 volts.
    J2a

  • J2-13 PLASMA MACHINE - EYE OF THE STORM

    J2-13
    Demonstrates electrostatic discharge
    This device is a commercial apparatus often used in magic shows or to enhance the look of a laboratory in a science fiction movie. When the machine is turned on a discharge occurs between the inner electrode and the outer glass; placing your hand on the glass draws the discharge but does not create a shock. The spark can also be controlled by ambient sounds. Prof. Dennis Papadopoulos has calculated that the operating voltage of this device is approximately 6 kV in the range of 20-40 kHz.
    J2b

  • J3-23 FARADAY CAGE - RADIOWAVES

    J3-23
    Demonstrates that radio waves cannot penetrate a Faraday cage
    The radio is tuned to a good station so that everyone can hear. Lowering the screen Faraday cage over the radio stops the radio waves, and the sound of the radio ceases.
    K8

  • J5-18: OERSTED EXPERIMENT

    J5-18
    Demonstrates that magnetic fields are generated around current-carrying wires
    A compass needle is mounted directly below a wire on a clear plastic sheet which is positioned on an overhead projector. When a current (provided by a battery and switch) flows in the wire the compass needle lines up perpendicular to the wire, showing that the current-carrying wire produces a magnetic field perpendicular to the wire. The action is viewed using an overhead projector. The two geometries are excited individually, as seen in the center (left coil) and right (right coil) photographs. However, notice that the compass near the wire that is not being excited is affected by current in the other coil.
    J5, PS1

    j5-18b j5-18a

  • J5-32: MAGNETIC LEVITATION - PERMANENT MAGNET AND ELECTROMAGNET

    J5-32
    Demonstrate magnetic levitation.
    A ring magnet levitates above an electromagnet, held in place horizontally by a plastic tube. Turn the power supply on and off for controlled levitation.

  • J6-01: ELECTROMAGNET WITH BANG

    J6-01
    Illustrate the force which can be exerted by a small electromagnet.
    An electromagnet operated by a single flashlight battery holds up an iron brick as in the photograph. Flip the switch off to allow brick to fall, awakening your students.
    J6

  • J6-04: LOW-POWER HIGH-FORCE ELECTROMAGNET

    J6-04
    Show that a small amount of energy can produce large magnetic forces
    A magnet and keeper are held together by energizing the magnet with a flashlight battery. It usually takes more than one person pulling on each side to separate the magnet and keeper.
    J6

  • K1-12 CATHODE-RAY TUBE - DEFLECTION BY MAGNET

    K1-12
    Demonstrates the force on an electron beam by a magnetic field
    The cathode ray discharge tube produces an electron beam moving from left to right, which can be seen on the fluorescent screen inside the tube. Holding a bar magnet close to the tube, parallel to the tabletop so that it produces a horizontal magnetic field inside the tube, causes the electron beam to deflect up or down. If the directions of the magnet's poles are reversed, the direction of the deflection should also reverse, illustrating the vector nature of the force.

    If desired, a video camera may be requested to display this demonstration on the projection screen in the large lecture halls.
    K1

  • K2-61 THOMSON'S COIL

    K2-61
    Demonstrates a number of concepts in magnetic induction
    A large vertical induction coil with a fixed iron core rests on a power supply base. The coil can be activated by a momentary switch, and a variety of induction effects can be shown.

    Some demonstrations that can be performed with this apparatus: (1) JUMPING RINGS: Placing a ring over the extended primary coil core and switching it on causes the ring to jump. A smaller ring will jump higher. Cool the ring in liquid nitrogen to get a really great jump, but be careful about hitting the rear projection screen. Broken metal rings and wooden rings are unaffected. (2) RESISTIVE HEATING: Verify that there is resistive heating in the secondary ring by having a student hold it down until it gets too hot to touch! (3) A light bulb on a small coil lights up when the coil is moved over the extended core. (4) A secondary coil with small light bulb placed in a beaker on top of the secondary coil will remain lit when it is covered by water in the beaker.

    To understand the force on the jumping ring one must account for its self-inductance, which causes an extra phase lag of the induced current. The AC current in the coil produces an alternating magnetic field, which induces an alternating current in the ring. The ring thus experiences an alternating vertical magnetic force, due to the radial component of the magnetic field. (One can also think of this as a force between the two currents, repulsive when they are parallel and attractive when they are opposite.) Without self-inductance of the ring, the induced current would lag the magnetic field by a quarter cycle, and the time averaged vertical force would vanish. The self-inductance causes an additional phase lag, hence a repulsive average force. See Jeffery & Amiri, "The Phase Shift in the Jumping Ring," TPT 46, 250(2008), for a detailed explanation.

    An interesting historical note: This device is named for its inventor, electrical engineer Elihu Thomson, not for his better known contemporary J. J. Thomson, whose work with CRTs led to the discovery of the electron.

    Water, liquid nitrogen for cooling rings, and related accessories can be available upon request.

    Thanks to Prof. Ted Jacobson for assistance with this explanation.
    K2

  • K2-62 CAN SMASHER - ELECTROMAGNETIC

    K2-62
    Blasts a soda can into two pieces using electromagnetism

    A 400 microfarad capacitor is charged to 3000 volts (1.8 kilojoules) and discharged through a three-turn coil into which an aluminum soft drink can has been positioned. With the circular windows open, the two pieces of the can will be blasted over thirty feet to the sides of the large lecture hall. Charging the capacitor to less voltage results in a can with a "waist."

    This device can be explained in two distinct ways:
    (1) The rapidly rising current creates a rapidly rising magnetic field along the axis of the coil, which in turn induces an electric field going in circles inside the coil. The induced electric field causes an electron current in the can which experiences a vxB force in the magnetic field of the coil, causing the can to break into two pieces which are blown to the opposite sides of the lecture hall.
    (2) A type of "theta pinch" phenomenon. More information on this is available from Wikipedia. Another way to understand this is that the induced current around the can is opposite to the current in the primary coil, since it is opposing the change in flux. These concentric opposite currents repel each other, so the can is pinched and torn apart and ejected out the sides.

    This is an UNFORGETTABLE DEMONSTRATION. A must when you cover electromagnetism.

    This video, from the Video Encyclopedia of Physics Demonstrations, shows the operation of the can crusher with an animation illustrating (1) the electron current in the coil, (2) the vector magnetic field that it creates, (3) the induced electric field within the coil created as the coil current rapidly rises, (4) the electron current circling in the can created by that induced electric field, (5) and the vxB force on the electrons moving around the can.

    Following a description of the crusher electronic components, the animation is displayed. The animation may be stopped so that the directions can be studied in detail for the five (5) quantities listed above. Using the left hand rule (for electrons) the directions can be verified; note that according to Lenz's law the direction of the electron current induced in the can must be in the opposite direction to the electron current in the coil.

    Note that the magnetic field at either end of the coil possesses both an axial and a radial component; the electron current in the can is entirely azimuthal. Using the left hand rule to determine the direction of the cross product of the electron velocity and the magnetic field, it can be seen that the axial component of the magnetic field leads to an inward force, crushing the can, while the radial field component leads to an axial force, away from the plane of the coil at both ends of the can, causing the two parts of the can to move rapidly away from the coil. (In the large lecture hall the two parts of the can will be blown to the sides of the lecture hall.)

    The web site http://hibp.ecse.rpi.edu/Can_Crusher/home.html contains a drawing and animation showing how the RPI electromagnetic can crusher works.

    FS1

  • K4-07 BICYCLE GENERATOR

    K4-07
    Demonstrates a 110 VAC magnetoelectric generator, and the relationship of work to power output

    Pedaling the bicycle generates 110 VAC, which can be used to light an array of five 110 volt 150 watt lights. The sum, totaling 750 watts or about one horsepower when fully lit, can be verified using the voltmeter on the generator housing.
    K4, FS1

  • K4-09: BICYCLE GENERATOR - LIGHT BULBs VS CFLs

    K4-09
    Compare brightness and power requirements of regular tungsten filament light bulbs and compact fluorescent lamps.
    Pedaling the bicycle generates 110 VAC, which can be used to light an array of four 110 volt 60 watt incandescent light bulbs. The sum, totaling 240 watts when fully lit, can be verified using the voltmeter mounted on the bicycle. Alternatively, switch in the array of 15 watt CFLs (compact fluorescent lamps) and use the bicycle generator to light them. These CFLs are equivalent in light output to the 60 watt incandescent bulbs. It is easy to notice that the same amount of light created by the standard light bulbs can be created relatively easily using CFLs. The upper two photographs above show Krishna pumping the bicycle generator to light the incandescent bulbs (top photograph) and the CFL bulbs (second photograph); the lower two photographs show the arrays of lamps plugged into the 110 VAC outlet in front of the bicycle. The third photograph shows the incandescent bulbs and the last one shows the CFLs being activated. The student volunteer for riding the bicycle will testify as to the increased effort required to light the incandescents over the CFLs. This is a dramatic demonstration and can be used very effectively in class.
    K4, FS1

  • K8-42: RADIOWAVES - ENERGY AND DIPOLE PATTERN

    K8-42
    Demonstrates transmission of energy in electromagnetic waves. Shows the radiation pattern of the dipole antenna

    This demonstration is centered on a simple radio transmitter with an antenna, which sends a signal to a handheld dipole antenna connected to a light bulb. The receiving antenna can be moved around in space, keeping the two antennas parallel, to observe the dipole radiation pattern. Rotating the receiving antenna to a vertical orientation shows that the radiowaves are polarized, as seen by the light going out.
    Background

    An antenna receives an induced current from the electromagnetic field of the passing wave. The dipole is a linearly polarized antenna, sensitive to signals oriented in a particular direction. In this experiment, we can see this dramatically, as changing the orientation of the antenna relative to the source produces a significant drop in signal strength, so that it is no longer receiving sufficient energy to light the bulb.

    Compare this effect to other wave and polarization demonstrations in sections G3 and M7.
    FS1