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Electromagnetic Induction

  • E2-11: SOLAR PLASMA MODEL

    E2-11
    Mass driver and ring heater show coronal holes and coronal heating.
    Hold down the ring to simulate confined plasma in a solar coronal loop; it will heat up much as does the solar plasma. Let the ring go and it will "shoot" away from the AC fields much like the plasma shoots out of coronal hole.
    K2

  • J2-33: TESLA COIL - PORTABLE

    J2-33
    Easy-to-use high-voltage device for use in various demonstrations or just to draw a nice spark.
    This is an easy-to-operate 110V/60Hz device that reliably produces a nice spark. It can be used to demonstrate discharge to grounded objects. Please handle carefully.
    J2b

  • J6-31: FORCE ON SOLENOID CORE

    J6-31
    Demonstrate the force exerted on the core of an electromagnet.
    When the switch is on, the force between the coil and the iron core suspends the coil and base a few centimeters off the table.
    K2, PW1

    j6-31a

  • J6-32: FORCE ON SOLENOID CORE - SMALL

    J6-32
    Demonstrate the force exerted on the core of an electromagnet.
    Turn on magnet and feel the force with which the coil is pulling the core into the center of the solenoid. Turn on magnet and feel the force with which the coil is pulling the core into the center of the solenoid.

  • 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

  • J7-24: BARKHAUSEN EFFECT

    J7-24
    Demonstrate flipping of magnetic domains in iron.
    A soft iron wire is positioned in the core of a large coil. The coil is attached across the microphone input of an audio amplifier, which in turn is connected to a loudspeaker. Hold the iron core fixed as you bring a small magnet near one end of the wire. Magnetic domains flip into alignment with the applied magnetic field as the magnet comes closer and the field increases. When a domain flips, it emits a short electromagnetic pulse which is picked up by the coil as a spike and heard as a click on the loudspeaker. To make the experiment more convincing, do it with a piece of copper wire and without any wire at all in the coil.

  • K1-41: BARLOW'S DISC

    K1-41
    Demonstrate how an electric potential difference and current can be generated when free (conduction) electrons move through a magnetic field.
    Rotating a copper disc between the pole tips of a strong C-shaped magnet, to create a vxB force on free electrons in the copper, creates a potential difference which is picked up by brushes at the center and the outside of the disc and displayed on the galvanometer. Reverse rotation of disc to invert current (center photograph).
    K1, D1, ME2

  • K2-01 EARTH INDUCTOR

    K2-01
    Induces an emf by moving a coil through Earth's magnetic field
    A large wire coil is connected to a projection galvanometer. Motion of the coil through the magnetic field of the earth induces an emf which is indicated on the meter. Alignment of the coil relative to the earth's magnetic field lines can be found which produces a maximum deflection of the coil, or almost no deflection. Optionally, a bar magnet (available upon request) can be thrust in and out of the coil to induce a larger voltage, illustrating the relatively low strength of the Earth's field.
    K2

  • K2-02 INDUCTION IN A SINGLE WIRE

    K2-02
    Demonstrates magnetic induction
    A single wire is connected to a projection galvenometer. Passing the wire quickly between the pole tips of a strong permanent magnet induces electric current, which is seen on the meter.
    K2, K1

  • 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

  • K2-04 FARADAY'S EXPERIMENT - EME SET - 20, 40, 80 TURN COILS

    K2-04
    Shows that the induced current is proportional to the number of turns in the secondary coil
    Three coils are connected in series with a projection galvanometer on an overhead projector. A bar magnet is thrust through one of the coils, inducing current in the coil which is shown on the meter. Three coils are included on the device: 20, 40, and 80 turns; the bigger the coil the greater the induced current.

    Have students try to predict the relationship between coil size and current strength before performing the experiment.
    K2, J5a

  • 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.

  • K2-22 INDUCTION COIL WITH LIGHT BULB

    K2-22
    Demonstrates megnetic induction with 110 VAC
    Closing the switch puts 110 VAC on the primary coil, which is coupled to the secondary coil (on top) by a ferromagnetic core. The induced current in the secondary coil lights the 110 VAC light bulb.

  • K2-28: DEMOUNTABLE TRANSFORMER - 10 KV ARC

    K2-28
    Demonstrate that a large voltage increase is attainable using a transformer.
    The 250-turn primary coil is plugged into 110 VAC. The turn ratio of nearly 100 produces a large secondary voltage which arcs across electrodes placed on the output of the 23,000-turn secondary coil.
    K3, PS1

  • K2-29: COIL AND MAGNET WITH LED SENSOR

    K2-29
    Demonstrate that the sign of the induced voltage depends on the direction of the field as well as whether the field is increasing or decreasing in magnitude.
    Two versions of this demonstration, shown in the photograph above, will be delivered. Each consists of red and green LEDs, which respond to the two possible directions for the induced voltage, connected aross a coil. When the magnetic flux through the coil is rapidly changed, one of the two LEDs activates, depending on the direction of the flux change. The flux through the coil at the left is changed by making or breaking the magnetic circuit; for the setup at the right the flux change is created by passing the magnet rapidly through the coil. An interesting effect can be obtained by dropping the magnet through the coil.

  • K2-41: LENZ'S LAW - ROLLING RODS

    K2-41
    Demonstrate eddy currents and Lenz's law
    Various rods and tubes, metallic or non-metallic, magnetic or non-magnetic, are rolled down a wooden ramp into the magnetic field of a strong horseshoe magnet. Wooden rollers are not affected by the magnetic field. Magnetic rollers (such as a steel tube) are immediately sucked into the magnet gap when they get close enough to the pole tips. When non-magnetic metal rollers roll into the magnetic field, eddy currents are generated in the rollers which oppose the motion. The roller will slow down dramatically as it enters the field, but eventually pass through.
    K2

  • K2-42 LENZ'S LAW - MAGNET IN ALUMINUM TUBE

    K2-42
    Demonstrates Lenz's law

    Two arrays of magnets, containing five strong disc magnets each with small aluminum spacers between the magnets, are dropped through a vertical aluminum tube. One set, having its poles North-to-South, has very little external field, and falls very quickly through the tube. The other set, having its poles arranged North-to-North, then South-to South, etc., has a large external field. A solid aluminum bar of the same size is also available for comparison.

    Background

    As the magnetic array falls, it induces large currents in the aluminum tube. According to Lenz's law, these currents interact with the falling magnet array so as to oppose its (falling) motion, and the array takes several seconds to fall about two meters through the tube. By comparison, the aluminum rod falls much more quickly. For advanced students, compare the two different magnetic arrays, to show the relationship between the amount of slowing and the changing flux. For the simpler form of the demonstration, just use the aluminum rod and the North-North South-South array (marked with a red dot) to maximize the difference.

    Optionally, a smaller portable handheld of this demonstration is available upon request, suitable for small groups.
    FS2

  • K2-43: LENZ'S LAW - PERMANENT MAGNET AND COILS

    K2-43
    Demonstrate Lenz's law
    Thrust one pole of a strong horseshoe magnet into a coil, or quickly withdraw it from inside the coil. A current is induced in the coil that opposes the motion of the magnet, and the reaction force on the coil results in the coil being either pushed or pulled in the same direction that the magnet was moved. Move the magnet in and out of the single turn aluminum coil. Disconnect the hook for the single turn coil. No current can flow so no force is created. Videos:
    K2

  • K2-44 EDDY CURRENT PENDULUM

    K2-44
    Shows the damping of pendula due to eddy currents

    Pendula with bobs of different materials and geometries are swung through the poles of a strong horseshoe magnet. The amount of damping is greater for those bobs in which strong eddy currents can flow. Bobs include, solid copper, copper loop, broken copper loop, laminated copper, copper with central hole, aluminum, and wood.
    Engagement Suggestion

    After showing the swing of the nonconductive (wood) pendulum, encourage students to make a prediction about what the copper disc will do.

    Ideas to ask them about as discussion prompts:
    • • Will it swing just the same,
    • • stop immediately in the magnetic field,
    • • slowly slow down after a couple of swings,
    • • or gain energy and swing higher/faster?
    Background
    As a conductive pendulum swings into the magnetic field, the changing magnetic flux induces electrical eddy currents in the metal. Some shapes (e.g. solid disc) offer more opportunity for these currents to form and grow. Outside of the magnetic field, these currents disappear at the magnetic flux does, but each pass through the magnet creates the currents again. This causes a gradual loss of kinetic energy in the pendulum.
    K2, K1