Magnet activities

Magnets and iron filings

• Bar magnet (2)
• Acetate transparency
• Iron filings
• Magnetic compass
• Cow magnet
• Suspension of Fe filings in parafin oil

1. Use a double-length bar magnet.  Tape it onto the bottom of an overhead transparency.  Predict the magnetic field patterns.
2. Sprinkle the filings onto the acetate and examine the field.
3. If the magnet were to be broken into two pieces, predict the field pattern for each resulting magnet.
4. Separate the magnets, tape them onto the bottom of a new acetate and test your hypothesis.
5. Investigate the deflection of a compass needle.  Test with both ends of a bar magnet.
6. 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.
7. Sprinkle iron filings onto the top acetate and test your hypothesis.
8. What is meant by the magnetic dip angle or "declination"?
9. 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

• Hook-up wire
• Magnetic compass
• 6 amp power source
• Cardboard
• Fe filings

1. 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.
2. Investigate the field near the wire with compasses when the "large" current flows through the wire.
3. Reverse the current and note the compasses.
4. Sprinkle the cardboard with Fe filings to examine the shape of the magnetic field.

Magnetic Deflection of Electrons

Preliminary experiments - qualitative

• Hook-up wire (3 meters)
• Hand-cranked generator
• Compass
• CRT (Berkeley Physics Lab)
• Helmholtz coils and power supply
• Bar magnet
• TEL 525 electron deflection tube
• Digital multimeters

1. Make a coil out of about 3 meters of hook-up wire.
2. Investigate magnetic field of coil with hand-cranked generator and compass
3. Investigate the deflection of electrons with permanent magnet and CRT
4. Investigate the deflection of electrons with CRT, coil powered by hand-cranked generator
5. 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
6. Set-up the quantitative apparatus for the magnetic deflection of electrons with the TEL 525 electron tube.

Electron Charge/Mass