Follow

PHYS270

  • K4-02 MAGNETOELECTRIC GENERATOR WITH LAMP

    K4-02
    Demonstrates a small 110 VAC magnetoelectric generator
    A small magneto-electric generator is connected across a simple incandescent light bulb. Crank the handle to light the bulb.
    K4

  • K4-21: ST. LOUIS MOTOR

    K4-21
    Demonstrate the structure and operation of a simple motor
    The St. Louis Motor is a simple two-pole DC induction motor with a split-ring commutator and permanent magnets. It operates with a 1.5V battery; the magnets are conventional bar magnets, and can be temporarily removed to demonstrate this.

    To connect the power and turn on the motor, attach the alligator clip to the terminal at the end of the battery housing. When not in use, keep the alligator clip attached to the frame of the motor for safety. Be aware that this motor can rotate very fast. Watch your fingers!

    Notably, this device was not a product of the St. Louis Motor Company, nor of someone named Louis; its developer, S. A. Douglass, was a turn-of-the-century high school teacher in St. Louis, Missouri. You can learn a bit more about the history of this design here: T. Greenslade (2011), The St. Louis Motor, TPT 49, 424

    K4

  • K7-01: RL CIRCUIT - 50 MICROSECOND TIME CONSTANT

    K7-01
    Illustrate RL time constant.
    A resistance box and an air-core coil (from K2-27) are used in an RL circuit. The inductance of the air-core coil can be calculated (if desired) and the time constant L/R calculated from the inductance and the resistance of the box. This can be compared with the experimental result. The signal source, a square wave of about 2000 Hertz, is displayed on the upper trace, and the current in the RL circuit on the lower trace. See circuit above.
    K2, K7, ME2, ME3

  • K7-02 RL CIRCUIT - L/R TIME CONSTANT

    K7-02
    Shows L/R time constant for a slow circuit
    A nine-volt battery is used to energize the LR circuit while the current through the LR system is observed on an oscilloscope. The system is then shorted and allowed to de-energize. This setup uses an approximately 6 kilohenry coil and about 12 kilohms series resistance to produce a time constant of about 1/2 second.

  • K7-03 INDUCTOR DELAYING A LAMP

    K7-03
    Demonstrates the timing of current in a switched inductor circuit
    An inductor and light bulb are connected across a battery with a switch. In parallel with this inductor and light bulb is a second identical light bulb. The separate light bulb will light immediately, but the light bulb in series with the inductor will be delayed in lighting until the current reaches a high enough level. The delay time is related to the L/R time constant of that leg of the circuit.
    K7, PS1

  • K7-04: RL CIRCUIT - FIELD COLLAPSE WITH FLUORESCENT BULB

    K7-04
    Demonstrate the magnitude of induced voltage
    A 9-volt battery is connected across a large inductor; pushing the red button disconnects the inductor from the battery and immediately connects it across a fluorescent light tube. Collapse of the magnetic field in the inductor induces a voltage large enough to cause the fluorescent bulb to flash - well over 100 volts, or over ten times the voltage of the battery.
    K7

  • K7-22: RLC CIRCUIT - 10 KHZ - DAMPED OSCILLATIONS

    K7-22
    Demonstrate damped oscillations in an RLC circuit.
    Using the circuit above with a 500-Hertz square wave, damped oscillations are shown on the dual trace scope. The upper trace is the applied square wave and the lower trace shows the damped oscillations produced each time the square wave changes. The circuit can be adjusted to obtain either underdamped, overdamped, or critically damped oscillations by changing the capacitance or the resistance. In the photograph above the horizontal scale is 250 microseconds per centimeter, the frequency of the square wave is 500 Hertz (period of 2 milliseconds), and the frequency of the damped oscillations is about 8000 Hertz (period of 125 microseconds). The capacitor is set to its maximum value and the resistor is set to about 20% of its maximum (20 kilohms).
    K7, ME2, ME3

  • K7-27: RLC CIRCUIT - COMPLETE

    K7-27
    Show the phase shift between components in a series RLC circuit.
    An RLC circuit has been constructed with linear isolation transformers to eliminate grounding when the circuit is attached to a four-trace oscilloscope. Using this device, the signals across the input, R, L, and C can be viewed simultaneously as the oscillator frequency is swept through resonance. The complete circuit diagram is shown above.
    K7, ME2, ME3

  • K8-01 ELECTROMAGNETIC WAVE - MODEL

    K8-01
    Shows the relationship between the electric and magnetic field vectors in a plane-polarized traveling electromagnetic wave
    Red pegs represent the electric field vector and blue pegs represent the magnetic vector. The spatial relationship between these vectors and the direction of propagation can be seen. By moving the model along its axis the temporal aspect of the wave can be shown. This wave has a wavelength of 0.81 meters, and as an EM wave would have a frequency of 370MHz
    FS1

  • K8-11: MICROWAVES - STANDING WAVES

    K8-11
    Demonstrate microwave standing waves.
    A standing wave is set up between the source and an aluminum sheet. The receiving antenna can be moved back and forth between the transmitter and the reflector to locate nodes (bottom) and antinodes (top). The wavelength is 12 cm, so the nodes (or antinodes) are 6 cm apart.
    K8

  • K8-12: RADIOWAVES - STANDING WAVES

    K8-12
    Demonstrate standing waves using radio waves.
    This demonstration uses a simple low-power RF transmitter with vacuum tubes, of a type developed by P. E. Klopsteg. A handheld dipole antenna with an indicator lightbulb at the center serves as the receiver. Set transmitter so that the antenna is parallel to the blackboard. (The blackboard is made of a painted metal sheet.) Hold the receiving antenna parallel to the transmitting antenna between you and the transmitter, and walk up the steps in the lecture hall. The bulb will produce maximum glow about every two meters, illustrating standing waves. This demonstration is only usable in classrooms PHY1410 and 1412.
    FS1

  • K8-13: RADIOWAVES - LECHER WIRE STANDING WAVES

    K8-13
    Illustrate standing electromagnetic waves in a high-impedance transmission line.
    Slide the fluorescent tube along the wires as shown. It will light up at the antinodal regions and remain dark at the nodal points of the standing wave along the transmission line.

  • 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

  • K8-45 RADIO WAVES FROM SPARK

    K8-45
    Demonstrates that a spark contains radio waves
    Turn the radio on to a frequency where there is no station. Hold the battery near the radio and short it out by quickly contacting and releasing the contact using a banana wire cable. A clicking sound will readily be heard on the radio.

    Compare J3-23: Faraday Cage - Radio Waves, which can use the same radio to illustrate a related phenomenon.
    K8

  • K8-51: MICROWAVE OVEN

    K8-51
    Demonstrate operation and experimentation with a microwave oven.
    A microwave oven is provided along with a number of accessories to carry out a variety of demonstration experiments. Some of the things that you can do include: (1) Use the small neon sensors to try to see the standing wave patterns of the microwaves in the oven, (2) Make a light bulb glow by turning on the oven, (3) Create artificial lightning discharges with a candle, (4) Make sparks with a CD. DANGER: If you heat water, be aware that it can become superheated, and explode after it is removed from the oven. Use caution in heating water.
    OS9

  • L1-11: INVERSE SQUARE LAW - LIGHT BULB AND RADIOMETER

    L1-11
    Demonstrate that light obeys the inverse square law.
    The intensity of the bulb as a function of distance can be measured by a radiometer, verifying the inverse square relationship. The radiometer reading is displayed using an overhead projector slave meter.
    OS0, ME2, OM1

    l1-11a

  • L2-01 OPTICAL BOARD - PLANE MIRROR

    L2-01
    Demonstrates reflection from a plane mirror

    This demonstration shows that the angle of incidence is equal to the angle of reflection. A bright white light source is directed through a baffle with several slits, producing a set of rays. Lenses are used to collimate these rays, and they are then reflected off of a long plane mirror. If the lenses are adjusted such that the incoming rays are approximately parallel, the reflected rays will be as well.
    Engagement Suggestion
    Optionally, you can use slits with colorful filters to show that this is good for all colors. Challenge students to predict what will happen if you switch to the color filters – will different colors reflect at different angles? Why or why not?
    Background
    Unlike light diffracted through a lens or prism, reflected light from a surface is unaffected by the frequency of the light. The reflection off of a flat mirror is dependent only on the angle the light strikes at. Thus, there should be no chromatic aberration in a reflecting telescope, one reason they are valuable for astronomical use.
    FS1

  • L2-05 PERVERTED IMAGE - AXES IN MIRROR

    L2-05
    Investigation of the nature of images from a plane mirror
    A plane mirror with three small coordinate axes, one left-handed and two right-handed. Position one right-handed coordinate system in front of the mirror and ask a student to line up the second right-handed coordinate system so that it looks like the image in the mirror. It will quickly be seen to be impossible. Try again with the left-handed coordinate system. That this can be done indicates that the mirror inverts one of the axes, but which one? Everyone agrees that the mirror does not invert top-to-bottom. Stand in front of the mirror and wiggle your right hand; the hand on the same side wiggles in the mirror, indicating no left-to-right inversion!
    L2, OS6

  • L2-06 MAGIC TRICK - DISAPPEARING RABBIT

    L2-06
    Plane-mirror magic trick


    A box has been divided diagonally by a flat mirror. A hatch in the top lets a toy rabbit be dropped in to the space behind the mirror.
    Engagement Suggestion
    • • The box is first shown to the group. Then the black cloth is placed over the front of the box, the trap door on top of the box opened, and the rabbit put into the box through the trap door.
    • • Invite students to predict what they will see when the cloth is removed.
    • • When the black cloth is removed the rabbit has vanished into thin air (behind the mirror).
    • • Challenge then to analyze how this has happened
    • • Explain the positioning of the mirror, and invite them to consider what it would look like with the mirror at different angles.
    Background
    Because the mirror is mounted at a 45 degree angle, it reflects the bottom of the box to look like the rear of the box. So viewed from the front, the box appears empty. This is a common technique for creating such illusions.
    L2

  • L2-22: INFINITY MIRROR

    L2-22
    Illusion with half-silvered mirror.

    A single square array of small lights has a full-silvered mirror in back and a half-silvered mirror in front. A long black box placed in back of the infinity mirror appears to have many rows of lights in it until it is removed!

    An interesting sidelight is to use this device to indicate the dynamic range of the eye. Each successive row of lights has an intensity of about 1/2. Approximately twenty rows of lights can be seen by the typical naked eye, so the dynamic range of the eye is at least as great as 2^20, or 1,048,576 to 1.
    L2, FS1

    l2-22a