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Magnetic Materials

  • I7-21: SUPERCONDUCTOR - MAGNET LEVITATION

    I7-21
    Demonstrate levitation of a magnet above a high-temperature superconductor
    A one-inch diameter superconducting disc is set on a conducting base in a bath of liquid nitrogen. A cubic samarium cobalt magnet levitates above the superconductor. Note that to show the Meissner effect you must place the magnet on the disc before cooling it down. When the superconductor passes through its transition temperature the magnet rises up by itself and levitates. For large groups, a camera can be provided.
    I7, I0

  • I7-23: Magnetic Track and Superconductor

    I7-23
    To illustrate levitation of a superconductor and magnetic pinning
    A chilled superconducting puck is levitated above a magnetic track. Despite the curve and slope of the track, the puck will remain above the track as it moves.

    This is an illustration of the diamagnetic and magnetic pinning effects of a superconducting material. When setting up, be sure to chill the puck in the position you want it above the track for maximum efficiency.

    The University of Cambridge has made available a helpful video lecture on magnetic pinning: https://ascg.msm.cam.ac.uk/lectures/fundamentals/pinning.php.

  • J5-01 MAGNETIC FIELD OF A BAR MAGNET

    J5-01
    Visualize the magnetic field around a bar magnet
    A bar magnet is positioned beneath a plastic box on an overhead projector. Sprinkle iron filings into the box above the magnet and tap the box slightly so that the filings will align along the magnetic field lines.
    J5a, J5b

  • J5-04: MAGNETS

    J5-04
    Show various magnets
    A varied collection of magnets is presented, including bar magnets, horseshoe magnets, disc magnets, ring magnets, and rare earth magnets. Ask about other types of magnets.
    J5

  • J5-06 MAGNET - BROKEN BUT NO MONOPOLE

    J5-06
    Demonstrates that magnet poles come in pairs
    The magnetic field of a bar magnet is demonstrated using iron filings on an overhead projector. The magnet is then broken and the demonstration is repeated. Each half of the original magnet has both poles
    J5

  • J7-01: LODESTONE

    J7-01
    Demonstrate the natural magnetism of lodestone.
    Bring a compass up close to the lodestone to demonstrate that it is magnetic.

  • J7-10: DIAMAGNETIC REPULSION OF WATER

    J7-10
    Demonstrate diamagnetism of water
    Water is repelled by a magnet. The effect is called diamagnetism. However, the effect is very weak. The orientation of the magnet doesn't matter; with either pole toward the water, the water is repelled. Atoms and molecules in which all of the electrons are paired with electrons of opposite spin and in which the orbital currents are zero, such as in helium, water, and bismuth, are diamagnetic. Bring a magnet toward a diamagnetic material, you will induce an electric current in the atoms of that material which make the atoms magnetic in a way that will repel the approaching magnet. (This is the same result as predicted by Lenz's law.) The glass is also diamagnetic and contributes to the repulsive effect.

  • 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

  • J7-12: CURIE POINT OF IRON

    J7-12
    Show the Curie point of iron.
    An iron wire is normally ferromagnetic, and therefore strongly attracted to the magnet as shown in the photograph. When heated so that it glows red hot by passing an electric current through it, the iron rises above its Curie point and loses its ferromagnetism, so springs at either end of the wire pull it away from the magnet.
    J7

    j7-12aj7-12b

  • J7-13 CURIE POINT OF NICKEL

    J7-13
    Shows the Curie point of nickel
    A Canadian nickel has the ferromagnetic element nickel as a major part of its composition, and is strongly attracted to a magnet. When heated above its Curie temperature by the gas torch, it loses its ferromagnetism and falls away from the magnet to the pedestal. After a few seconds it will again be pulled up to the magnet.
    J7, K1(magnet, bottom), I0

  • 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

  • J7-15: Paramagnetism of Dysprosium

    J7-15
    To illustrate room temperature paramagnetism
    Pendula of different materials are suspended here from a horizontal rod. As a large magnet is moved in next to them, we see an unsurprising response. The steel pendulum leaps over to the magnet; the wooden pendulum is entirely unaffected. There is a third pendulum, however, that appears to be slightly, but not very strongly, attracted to the magnet. The bob on this pendulum is a lump of dysprosium.
    This demonstration can be valuable used in conjunction with J7-14: Curie Point of Dysprosium, to show the change in dysprosium's behaviour at different temperatures. Encourage students to visualize the magnetic dipoles within the material and how they may change at this transition.

  • 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

  • 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.

  • J7-31: VISIBLE HARD DRIVE

    J7-31
    See what the guts of a fixed magnetic drive look like.
    At one gigabyte, this 3.5 inch hard drive was too small to be useful, so we cracked it open for all to see.
    J7

  • 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

  • K2-40: MAGNETIC ACCELERATOR

    K2-40
    Demonstrate magnetic potential energy
    A slightly curved track holds a series of steel balls. One ball, superficially similar to the others, is a magnet. To use: Fill the track with nonmagnetic balls, and release a single ball from one upper end of the track. It rolls down and across the track until is collides with a stationary line of balls. As expected, the last ball in the line moves out with slightly less speed than the incoming ball. Now repeat the demonstration, replacing the first stationary ball in the line with the magnetic ball and the result is quite different. The attractive force of the magnet adds energy to the system, in a quite dramatic fashion.

    A similar effect can be seen with C7-19: Gaussian Gun
    K2

  • K2-64: UNIPOLAR GENERATOR

    K2-64
    Demonstrate unipolar generation of DC voltage, which may involve an explanation other than electromagnetic induction.
    A strong (over 10 kilogauss) cylindrical magnet is rotated about its axis at 1725 RPM. Brushes positioned on the axis of rotation and the "equator" of the bar magnet (midway between the two poles) are attached to a digital voltmeter. An electrical potential of about 15 millivolts is measured. Reversing the direction of rotation or reversing the ends of the magnet causes the DC voltage to reverse in sign. An aluminum bar can be substituted for the magnetic one and rotated in the CW or CCW directions. Note that there is a small (about 0.1-0.3 mV) potential developed with this arrangement, probably due to contact potentials between the various materials in the system and the wires, similar to the potential developed in a thermocouple. The observed potential is the same for either rotational direction of the aluminum rod; it would likely be opposite in sign for opposite rotation direction if it were due to some sort of induction effect. The explanation of this device is perhaps problematic. Many people believe that because there is no change in flux in the wire loop this cannot be an electromagnetic induction effect; the only explanation lies in special relativity. Other theoreticians disagree.
    K2, ME2