Follow

Electromotive Force and Current

  • J4-24: FORCE ON DIELECTRIC IN ELECTRIC FIELD

    J4-24
    Demonstrate the force on a dielectric in an electric field.
    Two wire electrodes extend into a bath of dielectric oil, as seen in the photograph above. When a potential of 2500 volts is impressed between the wires a force is exerted on the dielectric in that region, causing the oil to rise between the two wires, as seen in the close-up photographs below.

    j4-24aj4-24b

  • J4-31 ENERGY STORED IN A CAPACITOR

    J4-31
    Demonstrates that energy is stored in a capacitor and how that energy may be used
    Three capacitors totaling 205,000 microfarads are charged to 15 volts. Closing the three switches one at a time (a) turn on the light, which decays exponentially, (b) turn on the bell, or (c) activate a motor which lifts the entire system up a few inches
    J4

  • K1-06: CURRENT BALANCE

    K1-06
    Demonstrate the force between two adjacent parallel currents.
    The device uses two parallel currents, the lower one stationary and the upper one which can move to and away from the stationary wire. Current in the wires causes a force between the wires which can be determined by balancing the moving current loop with a movable counterweight. The measured magnitude of the force can be compared with the measured value.
    K1, PS1

  • K5-01: PIEZOELECTRICITY

    K5-01
    Demonstration of a piezoelectric crystal.
    A small piezoelectric crystal is housed in a chamber with a lever on top. Pushing down on the handle stresses the crystal, producing piezoelectric charge which makes a small spark across two nail tips (first photograph), or can be displayed on the electroscope, as seen using the setup in the second photograph. A video camera can be provided upon request to display the device in large classrooms.
    K5, J1b

  • K5-02: PIEZOELECTRIC CRYSTAL - AUDIBLE

    K5-02
    Demonstrate that a piezoelectric crystal converts electrical impulses into physical vibrations.
    An audio frequency electrical oscillation from an audio oscillator (in this case a 3 KHz sine wave, generated by the oscillator shown at left above, and fed through an audio amplifier) is converted into a sound vibration by the piezoelectric crystal in the center of the mechanical apparatus at right above. This is a commonly technique commonly employed for creating ultrasound.

  • K5-03: PIEZOELECTRIC IGNITOR

    K5-03
    Show a commercial use for piezoelectricity.
    Squeezing the handle stresses the crystal, creating a voltage sufficiently high that it creates a spark. These devices are used for starting fires with gas stoves, etc. This device is primarily for display, not for igniting things in the classroom.

  • K5-04: PIEZOELECTRIC GUN

    K5-04
    Application of piezoelectricity to produce copious quantities of electric charge.
    Hold the bundle of nylon strings by the knot and stroke it with the silk, causing the strings to become charged and to spread out due to the electrostatic repulsion. Aim the gun at the spread out string, slowly pull and then release the trigger. When the trigger is pulled the string separates slightly more (same charge), but when the trigger is released it creates the opposite charge, discharging the string so that the string bundle collapses (right photograph).

  • K5-11: BATTERY MODEL

    K5-11
    Simple model of a battery using a human as the source of energy.
    The instructor acts as a "battery," raising the potential of the "electrons" (ball bearings or marbles). The electrical potential is expended as the balls flow down to a point of lower potential energy, whereupon the instructor (battery) raises them again to repeat the process. This serves as a simple schematic of the flow of energy in an electrical circuit.
    K5, FS2

  • K5-12 BATTERY AND CURRENT - WORKING MODEL

    K5-12
    Model of battery with circuit attached
    Though originally built as a toy, this device can be used as a model of an electric circuit attached to a battery. The "battery" raises the penguin "electrons" to a high potential. where they then progress through a "circuit" as they lose their potential. This model might indicate that a battery EMF provides energy which the carriers dissipate against resistance - the carriers do not speed up as they lose potential energy.
    K5

  • K5-13: ELECTRIC CURRENT - MODEL

    K5-13
    Indicate how electrons really flow through a conductor.
    Nails are driven into one side of an inclined plane in an orderly pattern, representing the lattice of a crystal, and into the other side in a random fashion, representing the polycrystalline structure of a metal. Ping pong balls represent free electrons traveling through the material. In spite of the much larger number of nails on the structured side, the balls move more quickly than through the random array of fewer nails. The slope of the inclined plane models the potential difference, and the interaction of the balls with the nails models the interaction of the free electrons with the ion lattice of the material.

  • K5-14: ELECTRIC CELL

    K5-14
    Demonstrate how an electric cell is formed.
    A container is filled with a dilute solution of HCl or diluted vinegar, and and a pair of electrodes is inserted into the electrolyte solution. The voltage is measured using the lecture meter or digital interface. The standard electrode pair is copper and zinc.
    K5, ME2

  • K5-16: CARRIER CURRENT DENSITY MODEL

    K5-16
    Model the density of carriers crossing a plane.
    Red vectors represent electron flow, blue plate is surface of interest with its vector area represented by the blue arrow. Then: dQ/dt = j . dA = j dA cos a = j dA(proj), with j = n q v(drift).
    J3