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  • J5-19: MAGNETIC FIELDS OF PARALLEL AND ANTIPARALLEL CURRENTS

    J5-19
    Show the magnetic fields of parallel and antiparallel current-carrying wires.
    Overhead projector projectuals have been constructed for parallel and antiparallel currents in wires. The difference between the magnetic fields in these two cases can easily be seen.

    j5-19a

  • J6-33: ELECTROMAGNETIC GUN

    J6-33
    Demonstrate the force on a solenoid core, and to contrast forces on magnetic and non-magnetic cores.
    This demonstration uses the coil from demonstration K2-22, but in an unusual configuration:

    (1) Insert iron core, displace it as far as possible toward the base, and apply current until the core reaches the center of the coil. The core will eject a few meters. (2) Insert copper core (hollow) about one inch forward of the center of the coil. Apply current to slowly eject the core. (3) Insert both cores about an inch forward of the center of the coil. Predict the results. Dramatic. Stand clear!!

    K2, PS1

  • K1-04: FORCE ON CURRENT IN MAGNETIC FIELD - PORTABLE

    K1-04
    Demonstrate the force on a current-carrying wire in a magnetic field.

    A wire is placed or held between the poles of a small horseshoe magnet. When the ends of the wire are connected to a 6-volt battery, the wire jumps out of the magnet. The current in the wire or the orientation of the magnet can be changed to investigate the directions of the vectors involved.
    Engagement Suggestion
    • Once students have seen what happens, encourage them to predict the results of reversing the direction of the flow of current. Then swap it around and show what happens. Have them discuss the results.
    • What if you flip the magnet itself over? Again, have them predict what will happen, then try the experiment and discuss.
    Background

    This illustrates the Lorentz force, or Laplace force, as predicted by Maxwell’s equations. A current flowing through a magnetic field experiences a force determined by the cross product of the current vector and the magnetic field.


    See demonstration K1-03 in this section for a larger version of this demonstration for classrooms.

  • K1-11: CATHODE RAY TUBE - DEFLECTION BY CURRENT

    K1-11
    Demonstrate visually the force between two parallel currents.
    The discharge tube produces an electron beam moving from left to right, which can be seen on the fluorescent screen inside the tube. Activating an electric current in an external wire held along the top of the discharge tube, parallel to the electron beam, deflects the electron beam a small distance up or down. If the direction of the current in this wire is reverse, the direction of the deflection will likewise reverse. This illustrates the vector nature of the force.

    The photographs above show the displacement of the beam when the positive current in the wire is running (a)left-to-right, at left above, and (b) right-to-left, at right above. This is a small effect; a picture with no current in the wire is reproduced at the bottom above for reference. Using the switch to turn the current ON and OFF while watching the beam shows the effect VERY clearly.

    If desired, a video camera may be requested to display this demonstration on the projection screen in the large lecture halls.
    K1, PW1

  • K1-13: CATHODE RAY TUBE - DE LA RIVE MAGNETIC EFFECT

    K1-13
    Illustrate bending of an electron beam in a magnetic field.
    The tube contains a point electrode at the top and a ring-shaped electrode at the bottom. A cylindrical bar magnet runs up the center axis. When powered up, an electron discharge starts at the top electrode and trails down to the ring at the bottom. When an additional 5V potential is applied to the bar magnet, as shown in the photo, the discharge precesses around the magnet.
    K1, P2, PS1

  • K1-31: MAGNETOHYDRODYNAMIC GENERATOR

    K1-31
    Illustrate magnetohydrodynamic forces.
    A shallow bowl of copper sulfate solution is placed in the (downward) magnetic field of a medium-strength horseshoe magnet. An electron current is created between the negative electrode band around the circumference of the bowl and the positive electrode at the center of the bowl. The resulting vxB force on the electrons creates counterclockwise rotation of the copper sulfate solution. Small pieces of paper are dropped onto the surface of the rotating liquid as an indicator.
    K1, PS1

  • K2-03 FARADAY'S EXPERIMENT ON INDUCTION

    K2-03
    Demonstrates the induction between two coils
    A primary coil is connected to a battery by a key switch, so that closing the switch causes current to flow in the coil and releasing the switch stops the current. Three secondary coils are connected in series with a galvenometer. The primary coil is positioned inside the secondary coil and the current in the primary turned on and off. When the current in the primary coil is turned on, a sharp spike of current appears in the secondary coil. There is no secondary current while the current in the primary remains on at a constant level. When the key is released the current in the primary coil ceases, creating a sharp current spike in the secondary coil of opposite sign to that produced when the primary current is started. The induced current is greater for a secondary coil with more turns. The experiment can be repeated with copper, aluminum, and iron cores. This uses the same coil and meter setup as K2-04; consider using them together to compare permanent magnets and electromagnetic coils.
    K2

  • K2-05: FARADAY'S EXPERIMENT - CONCENTRIC COILS

    K2-05
    Demonstrate mutual induction.
    Two square 1,000-turn coils are mounted one inside the other. The larger exterior primary coil is connected to a 6V battery and keyswitch; the interior secondary coil, to a projection galvanometer. Closing or opening the switch starts or stops current in the primary coil, inducing a voltage in the secondary which is seen by the galvanometer.

    Note that the primary coil is also used for demonstration K2-27: Mutual Induction - M21=M12; be prepared to swap components if using both demonstrations.

    K2, K4

  • K2-21: RUHMKORFF INDUCTION COIL

    K2-21
    Demonstrate induction of a very high voltage using a small voltage source.
    The Ruhmkorff coil is a classical transformer that uses a vibrating interrupter mechanism to create high-voltage pulses from a low-voltage direct current. They were widely used in industry and research in the late 19th and early 20th centuries, but are now largely used for educational purposes. Interestingly, automotive spark plugs are a descendant of this technology.

    In this experiment, a 7.5 volt battery is connected to the input of a high-voltage Ruhmkorff induction coil. The induced voltage will produce a 1"-2" spark. Note: Please be careful not to touch the electrodes until after the coil is fully discharged.

  • K2-48: EDDY CURRENT MOTOR`

    K2-48
    Show the use of eddy currents in producing a motor with few moving parts and no electrical brushes.
    An aluminum soda can is mounted on a rotating bearing, with the sawn-off cores of transformers mounted adjacent to the center of the can. When 110 VAC power is connected to the transformers, eddy currents cause the can to rotate.
    K2

  • K3-01: INDUCTION IN A TRANSFORMER

    K3-01
    Demonstrate that a change in the primary current induces a secondary voltage.
    A simple transformer is built from two demountable coils and an iron core. The 46-turn primary coil of the transformer is connected through a variable resistor to a 1.5 volt battery, and a large galvanometer or other measuring device is connected directly across the 500-turn secondary, as shown in the circuit diagram above. The primary current in this simple transformer circuit is changed by sliding the variable resistor contact, inducing a secondary potential which is indicated by the galvanometer. Motion of the resistor slider and current in the galvanometer are correlated.
    K3, ME2, PS1

  • K3-02: DEMOUNTABLE TRANSFORMER - SINGLE SPARKS

    K3-02
    Demonstrate induction of large voltages by a large secondary-to-primary turn ratio.
    A six-volt primary source is switched on and off to a five-turn transformer primary coil. The 23,000-turn secondary produces enough voltage to cause a significant arc between wires connected to the transformer secondary

  • 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

  • K4-08: 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

  • K4-24: 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

  • 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.

  • K5-14: 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

  • K5-21: AC PLUG CIRCUIT CHECKER

    K5-21
    Check the wiring of 110VAC power sockets.
    When plugged into a 110V AC outlet, this popular device can be used to detect some common wiring errors. A simple pattern of indicator lights communicates faults with polarity, grounding, and open connections. When using, be certain that it is fully inserted into the socket for consistent results.

    Consider ordering this in conjunction with K5-22, which provides some sample faulty outlets.

    circuit tester

  • K5-22: AC PLUG CIRCUIT CHECKER CHECKER

    K5-22
    Demonstrate several different kinds of AC outlet wiring error.
    The multiple outlet box has been modified so that a different kind of wiring error has been introduced to each of the sockets. (1) open ground, (2) open hot, (3) hot and ground reversed, (4) hot and neutral reversed, and (5) correct wiring. The response of the circuit checker to each type of error can be seen by plugging it in. (Note: Plugging this multiple outlet box into a wall socket will not blow a fuse.) Consider requesting a video camera for easy viewing.