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  • K5-32: RESISTANCE VS DIAMETER AND LENGTH

    K5-32
    Determine how resistance varies as a function of diameter and length for the same material.
    The resistance of two wires of the same length but different diameter can be compared. The resistance as a function of length can be determined by sliding the clips along the wire. Use of high-resistance nichrome wire keeps stray resistance (in contacts, etc.) small compared with the resistance being measured.
    K5, ME2

  • K5-34: THERMAL COEFFICIENT OF RESISTANCE IN COPPER

    K5-34
    Show that the resistance of copper changes linearly with temperature.
    Measure the resistance of the copper coil at room temperature (295K), at the temperature of a dry ice and methanol mixture (195K), and at the temperature of liquid nitrogen (77K). Plot resistance versus temperature to demonstrate the linearity.
    K5, I0, ME2

  • K6-23: HOT DOG COOKER - 110 VAC

    K6-23
    Illustrate the conversion of electrical energy into heat energy.
    A hot dog is mounted as shown in an overhead projection gizzit which skewers the hot dog between two nails connected to 110 VAC. The voltage applied to the hot dog and the current through the hot dog are displayed on the meters. The total energy can be found by plotting a graph of the current as a function of time and integrating. (Actually the current is pretty much constant so you can just take an average.) The initial and final temperatures are read by the digital thermometer, as seen in the photographs at the left and the right above. These pictures were taken using a fat-free vegetarian non-hot-dog. The cooking process is easier using a regular hot dog because the fat is an excellent electrical conductor. INSTRUCTOR MUST FURNISH ALL EDIBLE MATERIALS!!! Be sure to put the hot dog in the protective plastic shield provided so that grease will not splatter over the entire apparatus.

  • K7-14: RC CIRCUIT - 100 MICROSECOND TIME CONSTANT

    K7-14
    Demonstrate a reasonably fast RC circuit.
    Using a decade resistance box and a decade capacitor box a series RC circuit is produced. (1) It can be driven by a slow square wave (approximately 500Hz) and the voltage across the capacitor as the capacitor charges can be observed using the dual trace scope. (2) It can be driven by a sine wave (approximately 5kHz) and the phase shift between the voltage across the capacitor and the sine wave from the oscillator can be seen on the dual trace scope. See circuit above.

  • K7-21: RLC CIRCUIT - 10 KHZ - RESONANCE

    K7-21
    Demonstrate resonance in an RLC circuit.
    Using the circuit above, the frequency of the oscillator is swept to find the resonance. Both the signal from the oscillator and the signal across the resistor are displayed on the dual trace scope. The capacitor (0-300 picofarads) and the resistor (0-100 kilohms) in the circuit box are variable. The increase in amplitude of the signal across the resistor and the phase shift at resonance are both easily seen.
    K7, ME2, ME3

  • 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

  • K7-26: RLC CIRCUIT - 0.3 HZ RESONANCE

    K7-26
    Plot a graph of resonance behavior in a very low frequency resonant circuit.
    A series RLC circuit, containing a very large inductor, a 0-50 kilohm resistor, and a 100 microfarad capacitor is driven by a sine-wave oscillator as shown in the circuit above. As the frequency of the oscillator is varied between about 0.1 Hz and 0.5 Hz, the resonance in the system is observed to be about 0.3 Hz. The voltage across the capacitor is shown at various frequencies on an oscilloscope. The scope shows both the signal from the oscillator and the signal across the capacitor.

  • 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

  • K7-29: RLC CIRCUIT - 0.6 HZ TRANSIENTS

    K7-29
    Demonstrate transients using a circuit with a very long time constant.
    The circuit above is used to show transients of long duration. Closing the switch charges the capacitor, and opening the switch discharges it. The voltage across the capacitor is viewed using a storage scope. (Note: This demonstration is quite old and not always reliable.)

  • K7-41: RC CIRCUIT - DIFFERENTIATION AND INTEGRATION

    K7-41
    Demonstrate differentiation and integration using RC circuits.
    A series RC circuit is used to obtain the derivative or the integral of a periodic electronic signal. For differentiation the time constant of the series RC circuit must be very small compared to the period of the wave. The derivative is sensed as the voltage across the resistor (current in the circuit). For integration the time constant of the series RC circuit must be very large compared to the period of the wave. The integral is sensed as the voltage across the capacitor. Waves from a signal generator are input into the circuit, including sine wave, triangular wave, sawtooth, and square wave. The appropriate circuits are shown above.

    Note that these circuit elements are very small, and hard to see in a classroom. A camera may be requested to display them on screen in the large lecture halls.
    K7, ME2, ME3

  • K7-45: LOW AND HIGH PASS FILTERS

    K7-45
    Demonstrate use of a series RL circuit as a low-pass filter and a series RC circuit as a high-pass filter.
    The circuits above have been mounted on a plastic base for use with an overhead projector. Values of circuit components are shown on the projectual. In each case the input signal is input into the upper trace of the scope and the filtered signal into the lower trace. Complex waves can also be input to see how removal of some harmonics affects the wave shape.

    I: Low-pass filter with cutoff frequency f=R/L: The signal is input to the series RL circuit and the output is taken across the resistor.

    II: High-pass filter with cutoff frequency f=1/RC: The signal is input into the series RC circuit and the output is taken across the resistor.

    In this demonstration the experimental crossover frequency is about 5 kHz, so the biggest change in the amplitude of the signal is between 1 kHz and 10 kHz. In the sequences of photographs above the effect of the low pass filter (first sequence) and the high pass filter (second sequence) are shown at 1 kHz and 10 kHz respectively.
    K7, ME2, ME3

  • 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

  • K8-22: MICROWAVES - TUBULAR WAVEGUIDE

    K8-22
    Demonstrate transmission of microwaves in a tubular "waveguide."
    A microwave transmitter and receiver are separated by a distance of approximately 2 meters, and the transmitter is adjusted so that a weak signal is being received. Then a metal waveguide of approximately that length is slid into place, and it can be seen that the signal strength increases. If the receiver is then moved to the side of the waveguide, the shielding effect can be seen wherein the signal drops to nearly zero.

  • K8-32: PULSES IN TRANSMISSION LINES

    K8-32
    Demonstrate the reflection of pulses in terminated and unterminated transmission lines and to determine the speed of an electromagnetic wave in the transmission line.

    An oscillator produces narrow pulses (oscillator set to 1MHz, Div10 for pulses), which are input into the transmission line. The scope is triggered on the initial pulse, and the pulse is displayed on the top trace of the dual trace scope as it enters the transmission line and as it returns. The pulse at the end of the transmission line may be displayed on the bottom trace if desired.

    For a short section of transmission line the input and output pulses almost line up. Using about 100 feet of transmission line the delay is approximately 150 ns; for the test cable v/c was approximately 0.67 so the wave time is about 1.5 nanosecond per foot.

    To see reflections, use only the top trace. The far end can be left open, shorted, or terminated with a 50 ohm terminator to prevent reflection, as shown in the center two photographs above.

    The photographs below these two show the oscilloscope showing the 10 MHz pulse train (left), reflections with the far end of the cable connected to the lower trace of the oscilloscope, with the horizontal scale 250 nanoseconds per division (left center) and 100 nanosecond per division (center), the far end terminated by 50 ohms (right center), and the far end shorted but not connected to the oscilloscope (right).

    This demonstration makes an excellent companion to K8-04: Speed of Light which uses a similar technique to time a light pulse reflecting in air.
    K8, ME2, ME3

     

  • K8-43: RADIOWAVES - FREQ MEASUREMENT WITH OSCILLOSCOPE

    K8-43
    Experimentally determine the frequency of the radiowave transmitter.
    The signal from a radio frequency transmitter (mounted on a small stand) is picked up by the receiving antenna conencted to anoscilloscope. From the measured period of the radiowaves on the scope the frequency can be calculated. In the above photo, the period of the radiowaves is slightly greater than 12 nanoseconds, so the frequency is about 80 MHz. The transmitter should be located about 2 meters away from the receiving antenna to reduce the signal level to a readable amplitude for the scope.

  • L1-22: OPTICAL BOARD - PINHOLE CAMERA

    L1-22
    Demonstrate how a pinhole "image" is formed.
    The camera is represented by the region between the two baffles on the optical board. The left baffle has a small slit representing the pinhole, and the right baffle has a light surface to make the ray visible. Hold the carousel projector by hand and shine it at the "camera." from a position at the left of the optical board. The position of the source and the position of the "image" are related.

  • L2-27: Infinity Mirror - Portable

    L2-27
    Illusion with half-silvered mirror.

    This is a smaller, more easily portable version of demonstration L2-22, suitable for use in small classrooms. A ring of lights is repeatedly reflected by a rear mirror and a partially silvered front window, creating the illusion of lights vanishing into the distance.
    L2

    L2-27: mirror device illuminated on table, showing shallow housing for lights behind mirrored face

  • 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

  • L3-17: FOCUSING OF HEAT WAVES - ARC LAMP AND PARABOLIC MIRROR

    L3-17
    Demonstrate focusing of heat waves by a concave mirror.
    The arc lamp with condenser lens produces a nearly parallel beam of heat. The parabolic concave mirror focuses the heat onto the match head, lighting the match in about ten seconds from a distance of about ten feet.

    l3-17a

  • L3-25: IMAGE LOCATION WITH TV CAMERA - CONCAVE MIRROR

    L3-25
    Locate the image position for a concave mirror.

    Focus the TV camera on the image of its lens created by the concave mirror (or the "X" printed on a paper mounted on the lens). Move the ruler toward the mirror until it is in focus, demonstrating that the image is at that point. The pictures below show the meter stick too close to the camera, at the focus of the camera, and too close to the mirror. The background consists of a large amount of unrelated physics demonstration equipment.

    l3-25a

    l3-25b

    l3-25c