Magnet activities
Magnets and iron filings
Supplies
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Bar magnet (2)
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Acetate transparency
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Iron filings
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Magnetic compass
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Cow magnet
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Suspension of Fe filings in parafin oil
Instructions
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Use a double-length bar magnet. Tape it onto the bottom of an overhead
transparency. Predict the magnetic field patterns.
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Sprinkle the filings onto the acetate and examine the field.
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If the magnet were to be broken into two pieces, predict the field pattern
for each resulting magnet.
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Separate the magnets, tape them onto the bottom of a new acetate and test
your hypothesis.
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Investigate the deflection of a compass needle. Test with both ends
of a bar magnet.
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Simulate the magnetic field of the earth with an overhead projector.
Place a magnet underneath a circular cardboard disk to simulate the spherical
earth. Predict the magnetic field of the earth based on this model
with a drawing.
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Sprinkle iron filings onto the top acetate and test your hypothesis.
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What is meant by the magnetic dip angle or "declination"?
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Place a "cow" magnet in a stoppered test-tube and immerse the assembly
into a suspension of Fe filings in paraffin oil.
Electric currents and magnetic fields
Supplies
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Hook-up wire
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Magnetic compass
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6 amp power source
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Cardboard
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Fe filings
Instructions
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Connect a hook-up wire to a current source (6 Amperes), run the current
in a vertical wire, the wire passing through a cardboard. Predict
the magnetic field associated with the straight-line current.
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Investigate the field near the wire with compasses when the "large" current
flows through the wire.
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Reverse the current and note the compasses.
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Sprinkle the cardboard with Fe filings to examine the shape of the magnetic
field.
Magnetic Deflection of Electrons
Preliminary experiments - qualitative
Supplies
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Hook-up wire (3 meters)
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Hand-cranked generator
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Compass
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CRT (Berkeley Physics Lab)
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Helmholtz coils and power supply
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Bar magnet
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TEL 525 electron deflection tube
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Digital multimeters
Instructions
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Make a coil out of about 3 meters of hook-up wire.
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Investigate magnetic field of coil with hand-cranked generator and compass
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Investigate the deflection of electrons with permanent magnet and CRT
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Investigate the deflection of electrons with CRT, coil powered by hand-cranked
generator
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Connect Helmholtz coils in series and hand-cranked generator and explore
with compass. Make sure the coils are connected in same sense, so
the magnetic field adds. Graduate to power the coils with power supply
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Set-up the quantitative apparatus for the magnetic deflection of electrons
with the TEL 525 electron tube.
Obtain data
For several accelerating voltages (2.0 kV to about 4.5
kV), measure the current in the Helmholtz coils to make the deflection
of the electron beam at either +2.4 cm at the edge of the card or -2.4
cm. Repeat for current in the opposite direction of the Helmholtz
coils. For each accelerating voltage use the average current.
Finish the calculations to obtain e/m for the electron
based on the written hand-out.