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Electromagnetic Induction

  • K4-05: MAGNETOELECTRIC GENERATOR WITH METERS AND LOADS

    K4-05
    An AC generator with rectifier, meters and several loads.
    The current vs. voltage relations can be observed for various loads using built-in meters. A bridge rectifier is used to feed a DC motor which lifts a 1 kg mass. An individual turning the generator crank can feel the effect of the load.

  • K4-06: MAGNETOELECTRIC GENERATOR WITH CAPACITOR

    K4-06
    Demonstrate that the generator is producing electrical energy, and that the capacitor stores electrical energy; also that a generator can run in reverse as a motor.
    The capacitor is charged up by cranking the generator. The generator is then run as a motor by energy stored in the capacitor.

    Ask your students the following brainteaser question: If you charge the capacitor by cranking the generator, what will happen when you stop cranking and release the handle of the generator? (a) It will continue to rotate in the same direction, (b) It will rotate in the opposite direction, (c) It will remain at rest.

    For discussion: Have students decide for themselves what form of energy is being stored here. Rotational energy? Electrical? Magnetic?

    K4

  • 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

  • K4-08: MAGNETOELECTRIC GENERATOR WITH INDUCTOR

    K4-08
    Demonstrate how a magnetoelectric generator stores energy in an inductor and how that energy is returned to the generator.
    A "Genecon" hand-cranked motor-generator is used to store energy in the large inductor from demonstration K2-11. While the handle is being cranked, it is stopped and immediately released.

    A question for the students: What will the handle do? (a) continue to move in the same direction, (b) reverse, and move in the opposite direction, or (c) immediately stop and not move at all.

    Note: When preparing to use this demonstration, make certain that the attached knife switch is open, or it will short out the generator and damage it (as well as failing to demonstrate induction).

    K4, K2

  • 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

  • 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

  • K4-22: DC MOTOR

    K4-22
    Show how a DC motor works.
    The AC/DC generator is used in reverse as a motor. A 4 volt power supply is connected across the rotating coil through the split-ring commutator, the 1.5 volt battery is connected to the permanent magnet by pressing a switch on the chassis, and the coil is given a bit of a push to start it rotating.
    K4, PS1

  • K4-23: AC MOTOR - SYNCHRONOUS

    K4-23
    Demonstrate the concept of a synchronous motor.
    The power supply, operating at 8 volts, is connected to the armature coil through the double-ring comutator. The current reversing switch is used with the armature coil. Reverse the current twice per rotation as the device operates. This is tricky; you will have to practice to be able to get the rotation in sync with your manipulation of the current reversing switch.
    K4, PS1

  • K4-24: AC/DC MOTOR

    K4-24
    Demonstrate the construction and the operation of AC and DC motors.
    This setup can be used to create either an AC or a DC motor. Connect 8 volt DC power supply, through a DPDT crossover switch, both to the field coils, and to the armature coils through one of the two commutators.

    A DC motor uses the split ring commutator. Turn on the power supply and start with a small push. Reversing the polarity of the power supply reverses the direction of the motor. The armature voltage can be seen on the meter.

    An AC motor uses the double-ring commutator. Reversing the switch twice per rotation of the coil mimics an AC power source.

    NOTE: Please avoid destruction of the coils; turn off the power supply when you are through.

    K4, PS1

  • K4-25: DC MOTOR - HOMEMADE

    K4-25
    Illustrate possibly the world's simplest motor.
    A small coil is mounted across the terminals of a battery as shown. The enamel is scraped off half of the coil wire where it contacts the battery terminals. The magnet is oriented such that when the coil is rotating it either pushes away or pulls toward the magnet in the appropriate part of its cycle. The other half-cycle the enamel prevents the coil from being activated; if it were it would counteract the torque which produces the desired rotation.
    K4, PS1

  • K4-41: MOTOR-GENERATOR PAIR

    K4-41
    Demonstrate that a motor and a generator are the same.
    A pair of identical motor-generators are connected together. Cranking either one as a generator makes the other one rotate as a motor. Reversing the direction of cranking the generator reverses the direction of the motor.

    This helps to illustrate the concept that motors and generators are basically the same apparatus used in different ways. Students may recognize this concept as it relates to ideas like regenerative braking.
    K4

  • K4-51: UNIPOLAR MOTOR

    K4-51
    Demonstrate a very simple unipolar motor.
    A "motor" is formed as shown in the large photographabove: a cylindrical magnet (with its field along the axis of the cylinder, is stuck to the head of a nail with a small aluminum flag between the two, as seen in the secondary photograph above. The tip of the nail is then held by the magnetic field onto the positive end of a battery. A wire soldered to the negative end of the battery is then touched to the magnet, creating a current loop. The vxB force causes the nail and magnet to rotate clockwise (as viewed from above). The diagram illustrates the direction of flow.
    K4

  • K6-42: SINE WAVE AND RECTIFIED SINE WAVE

    K6-42
    Show the AC output from a generator and how it is converted to full-wave rectified AC using a split ring commutator.
    This uses the large hand-cranked generator and an oscilloscope to actually see the shape of the voltage versus time produced by the generator. The double ring commutator puts out AC; the split ring commutator puts out full-wave rectified DC, as seen in the photographs above.

  • K7-05: SERIES MOTOR AND LIGHT BULB CONUNDRUM

    K7-05
    Generate thought about how a motor works.
    A 1.5 volt motor and 1.5 volt light bulb are wired in series such that a 1.5 volt battery can be connected across either of them individually, or across both in series. The first mpeg video linked below shows what happens when each is connected to the battery individually.
    Ask the students what will happen when both are connected in series: Will (a) only the light bulb operate, (b) only the motor operate, (c) both operate, or (d) neither operate?
    Again, only the motor spins, as seen in he second mpeg video below.

  • K7-61: TESLA COIL

    K7-61
    Demonstrate a tesla coil, including how magnetic induction and a resonant RLC circuit is used in the production of high-voltage high-frequency sparks.
    Our Tesla coil, circuit above, uses a 5000 volt transformer to charge a large oil capacitor. When the potential across the capacitor reaches the breakdown potential of the spark gap, breakdown across the gap occurs. The spark gap then becomes a conducting part of the RLC circuit, which resonates at a frequency of about 200 kilohertz. The large coil in the resonant circuit is the primary of the final transformer and the very fine coil is the secondary, producing about 200,000 volts at 200 kilohertz.
    Identify the components of the coil from the close-up of the figure at the right above.
    In the photograph the wires known as JACOB'S LADDER have been attached to the output terminals of the Tesla coil. A fluorescent light held by one end with the other end near the secondary coil will light by induction.
    DANGER: THE LOW VOLTAGE SECTIONS OF THIS DEVICE HAVE LETHAL CURRENTS.