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PHYS270

  • J5-18: OERSTED EXPERIMENT

    J5-18
    Demonstrates that magnetic fields are generated around current-carrying wires
    A compass needle is mounted directly below a wire on a clear plastic sheet which is positioned on an overhead projector. When a current (provided by a battery and switch) flows in the wire the compass needle lines up perpendicular to the wire, showing that the current-carrying wire produces a magnetic field perpendicular to the wire. The action is viewed using an overhead projector. The two geometries are excited individually, as seen in the center (left coil) and right (right coil) photographs. However, notice that the compass near the wire that is not being excited is affected by current in the other coil.
    J5, PS1

    j5-18b j5-18a

  • J5-20 OERSTED EXPERIMENT- LARGE COIL AND COMPASS

    J5-20
    Demonstrates that magnetic fields are generated around current-carrying wires
    The compass is positioned within the coil. When current is run through the coil the compass lines up along the axis of the coil in the direction of the magnetic field.
    J5, PS1

  • J5-30: OMEGA LEVITRON

    J5-30
    Show an interesting demonstration of magnetism.
    The Levitron floats in mid-air by the forces exerted by two opposed permanent magnets. Once set in motion, it's stabilized in space through the gyroscopic effect that the spinning produces, and will stay levitated for a minute or more (if you're lucky).

  • J5-32: MAGNETIC LEVITATION - PERMANENT MAGNET AND ELECTROMAGNET

    J5-32
    Demonstrate magnetic levitation.
    A ring magnet levitates above an electromagnet, held in place horizontally by a plastic tube. Turn the power supply on and off for controlled levitation.

  • J5-33 TORQUE ON A BAR MAGNET

    J5-33
    Demonstrates the torque on a bar magnet in a magnetic field
    A small bar magnet is suspended on a rotating pivot between the poles of a horseshoe magnet. If the bar magnet is turned and released it rotates back to its original position due to the torque applied by the magnetic field of the horseshoe magnet.
    J5b

  • J5-35: MAGNETS INTERACTING ON PIVOTS

    J5-35
    Show the interaction between two bar magnets
    Start the larger bar magnet rotating to watch the reaction of the lighter magnet.
    J5b

  • J5-36: MAGNETIC SPINNER

    J5-36
    Demonstrate magnetic levitation.
    Axle with two magnets mounted on it levitates above a magnetic base as it spins.

  • J5-51: GAUSSMETER

    J5-51
    Demonstrate use of a gaussmeter
    This is a Hall probe gaussmeter of research quality. It can measure fields from a fraction of a gauss to over 10 kilogauss (1 Tesla). Radial (the flat one) and axial (the cylindrical one) probes are included. Ask for magnets (Demonstration J5-04: MAGNETS) and measure their fields with a gaussmeter.
    J5, K1

  • J6-01: ELECTROMAGNET WITH BANG

    J6-01
    Illustrate the force which can be exerted by a small electromagnet.
    An electromagnet operated by a single flashlight battery holds up an iron brick as in the photograph. Flip the switch off to allow brick to fall, awakening your students.
    J6

  • 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

  • J6-33: 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

  • J7-11 PARAMAGNETISM AND DIAMAGNETISM

    J7-11
    Demonstrates paramagnetic and diamagnetic materials
    A sample of copper sulfate, a paramagnetic material, is slightly attracted to a magnet. A sample of bismuth, a diamagnetic material, is slightly repelled by a magnet. Samples of copper sulfate and bismuth are balanced on a light dowel rod hanging by a strip of plastic audio recording tape. The 2-kilogauss horseshoe magnet is used to push and/or pull the samples around, illustrating the small paramagnetic and diamagnetic forces.
    J7

  • J7-14: CURIE POINT OF DYSPROSIUM

    J7-14
    Show the Curie point of dysprosium, a normally non-magnetic material.
    Dysprosium is non-magnetic at room temperature. When a dysprosium sample is cooled to the temperature of liquid nitrogen, it passes through its Curie point, becoming ferromagnetic. The dysprosium sample in the photograph has been cooled in liquid nitrogen and is strongly attracted to the magnet. As it warms, it passes the Curie point, becoming non-magnetic and falling into the liquid nitrogen bath, which cools it so that it becomes magnetic and is attracted to the magnet, where it warms up, etc....
    J7, K1 (magnet, bottom), I0

  • J7-21: HYSTERESIS

    J7-21
    Demonstrate the hysteresis loop for an iron transformer core
    This demonstration shows the standard hysteresis curve with the magnetic induction B plotted on the vertical axis and the applied field H plotted on the horizontal axis. The value of H is obtained by using the voltage across a 1 ohm resistor in series with the 250 turn primary coil of the transformer. The value of B in the core of the transformer is obtained as the voltage across a capacitor in series with a resistor and the 500 turn secondary coil of the transformer. A variac adjusts the primary voltage so that the interesting parts of the hysteresis loop can be seen.

  • J7-23: MAGNETIC DOMAINS - MODEL

    J7-23
    Model the behavior of a magnetic material in a magnetic field.
    The array of compasses, representing magnetic domains in a sample of magnetic material, is positioned in the center of the Helmholtz coils on the overhead projector. Using a small bar magnet the compasses are de-aligned into a state of relative disorder. As the field of the Helmholtz coils is increased, more of the small magnets flip into alignment with the applied field. This is a model of the domains flipping into alignment in a sample of magnetic material as the magnetic field is increased. This effect, known as the Barkhausen effect, is shown directly in Demonstration J7-24: BARKHAUSEN EFFECT.
    OS9, J5, PS1

    j7-23aj7-23bj7-23c

  • K1-02: FORCE BETWEEN CURRENT-CARRYING WIRES - PROJECTION

    K1-02
    Demonstrates the force between two adjacent parallel current-carrying wires
    A pair of wires are mounted in an overhead projectual, as seen without any current flowing in the photograph above. The projectual can be wired to carry parallel currents or antiparallel currents. Connect power supply to the desired wires, one set at a time. With the red and black connectors (at right in the photo above) hooked up in series, the current will be antiparallel. With a shunt joining those two connectors, the two wires can be run in parallel, with one cable connected to each end.

    Students should clearly see that parallel currents attract and antiparallel currents repel.

    Note that it is very important not to run the power for more than a second, less if possible! The device can easily overheat and be damaged.
    J/K

  • K1-03 FORCE ON CURRENT IN MAGNETIC FIELD

    K1-03
    Demonstrates force on a current-carrying wire in a magnetic field

    A wire (reinforced by a plastic tube for safety) passes between the pole tips of a strong magnet. When the key is pressed so that current flows in the wire, the wire jumps out from between the pole tips.
    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 the leads 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 K1-04 in this section for a more portable version of this experiment.

    K1

  • K1-05: FORCE BETWEEN CURRENT-CARRYING COILS

    K1-05
    Demonstrate that current-carrying coils produce magnetic fields and interact like bar magnets
    Two coils are aligned with their currents moving around in the same direction, so their magnet fields will be North-to-South. They will attract each other when the current is started by pushing the switch (click here for video). Reversing the wires on the top can put any combination of magnetic poles adjacent, getting either attraction or repulsion (click here for video). A small bar magnet, included with the demonstration, can be used to see the forces between one of the coils and the magnet, again using any combination of magnetic poles (click here for video).
    K1

  • K1-12 CATHODE-RAY TUBE - DEFLECTION BY MAGNET

    K1-12
    Demonstrates the force on an electron beam by a magnetic field
    The cathode ray discharge tube produces an electron beam moving from left to right, which can be seen on the fluorescent screen inside the tube. Holding a bar magnet close to the tube, parallel to the tabletop so that it produces a horizontal magnetic field inside the tube, causes the electron beam to deflect up or down. If the directions of the magnet's poles are reversed, the direction of the deflection should also reverse, illustrating the vector nature of the force.

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

  • K1-21 TORQUE ON CURRENT LOOP IN MAGNETIC FIELD

    K1-21
    Demonstrates the torque on a current loop in a magnetic field
    A few-turn coil is positioned in the magnetic field of a small horseshoe magnet, as shown in the photograph. Pushing the switch connects the battery to the coil, passing electrical current through the coil and creating the torque, which is visible as a small rotation of the coil about its axis. Reversing the coil leads reverses the direction of the torque.

    A video camera can be made available upon request for displaying this demonstration in large lecture halls.
    K1