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PHYS122

  • 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

  • J5-05: MAGNET MODEL - FIELD LINES

    J5-05
    Visualize the magnetic field of a bar magnet.
    A bar magnet is placed on an array of small compass needles on an overhead projector. The array of compasses maps out the magnet field of the bar magnet.
    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

  • 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

  • J6-04: LOW-POWER HIGH-FORCE ELECTROMAGNET

    J6-04
    Show that a small amount of energy can produce large magnetic forces
    A magnet and keeper are held together by energizing the magnet with a flashlight battery. It usually takes more than one person pulling on each side to separate the magnet and keeper.
    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

  • J7-01: 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

  • J7-13 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

  • 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

  • K1-12 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

  • 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