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Semiconductors and Tubes

  • K5-23: ROTATING TWO-COLOR LED

    K5-23
    Demonstrate that what comes out of a 110 VAC plug is in fact alternating current.
    The bi-color LED is wired across the 110 VAC line. When current flows one direction the red side glows, and when current flows the other direction the green side glows, so if it is viewed from a distance the color appears yellow. When the device is swung in a circle the alternating colors become easily visible, indicating that the current in the line is alternating direction. This new and improved version of the device was created by Prof. Steven Rolston.

    Try showing the class the light while it is stationary, then explain how it works and have them predict what it will look like in motion.

  • K5-41: V-I CURVES FOR OHMIC AND NON-OHMIC DEVICES

    K5-41
    Illustrate resistive properties of resistors and diodes.
    A signal generator set to 500 Hz is used as the source of AC current feeding a series circuit with a shunt resistor and one other "test" circuit component, which can be either a resistor or a diode. The current is displayed on the vertical axis of the oscilloscope as the voltage across a shunt resistor. The voltage across the second element (the element under study) is displayed on the horizontal axis. As seen in the photograph above, the diode is non-ohmic. The breakdown potential of the diode can be observed. The polarity of the vertical input must be inverted in this demonstration due to grounding of the point between the two circuit elements.

  • K5-42: TRANSISTOR

    K5-42
    Demonstrate a transistor circuit.
    A high-current transistor controlled by a flashlight battery operates an automobile headlamp by switching a 7.5volt heavy duty dry cell onto the light. The circuit for the system is shown above, and is included with the demonstration. By removing and replacing wires it can be shown that the flashlight battery alone cannot operate the light and that the heavy duty dry cell connected directly to the light turns the light on.

  • K5-45: SEMICONDUCTOR MODEL

    K5-45
    Model of semiconductor.
    Nails are driven into the board in straight rows, so that the balls can roll down the slope relatively unimpeded. In this case, the apparatus simulates the motion of charge carriers in semiconductors under the action of an electric field. The field is increased by changing the tilt of the board.

  • K6-41: DIODE RECTIFIERS AND FILTERS

    K6-41
    Demonstrate rectification of 60 Hz AC by a diode and by a bridge rectifier.
    This demonstration exhibits two ways to rectify an oscillating signal into an approximately continuous voltage. As seen in the circuits above, a single diode can be used as a half-wave rectifier, or a bridge rectifier can be used as a full-wave rectifier. An inductor and a capacitor are used to filter the ripple from the resulting output. A load must be present for the circuit to work properly. Note: Connecting the terminal marked "inductor" shorts out the inductor, removing it from the circuit; but connecting the outputs marked "capacitor" puts the capacitor into the circuit.

    Arranged above are sets of pictures for each of the two rectifiers: half wave (diode) and full wave (bridge) rectifier circuit. Left to right, each set includes (1) the setup, (2) the output with no filtering, (3) the output filtered by the inductor only, (4) the output filtered by the capacitor only, and (5) the output filtered by both the inductor and the capacitor.