Download Lab 9 Force Fields

Lab: Force Fields – Action at a Distance
(Electricity and Magnetism)
Introduction: Write an explanation for each of the phenomena demonstrated.
1. .
2. .
Part 1: Demonstrating forces that act at a distance
Investigative Question: How can we predict the behavior of samples of matter that
are electrically charged or magnetic?
Materials: Pith balls, wool rags, plastic wands or combs, shredded paper, running
water, various magnets (compasses, bar magnets, ring magnets, neodymium disc
magnets, cow magnets), BBs
Procedures:
1. Suspend a pair of pith balls from threads so that they are separated by a distance
of approximately 2 cm. Rub a plastic wand with a wool rag (or run a plastic comb
through your hair) and touch it to one of the pith balls. Record your observations.
2. Suspend a pair of pith balls from threads so that they are separated by a distance
of approximately 2 cm. Rub a plastic wand with a wool rag (or run a plastic comb
through your hair) and touch it to one of the pith balls, then do the same to the
other ball. Record your observations.
3. Hold the rubbed plastic near the metal pole of an electroscope. Record your
observations.
4. Find other materials that are attracted or repelled by the rubbed plastic.
5. Try placing different pairings of magnets near each other to detect forces acting
between them. Can you demonstrate forces of attraction and forces of repulsion?
Can you demonstrate that these forces are able to “pass through” matter? What
types of materials are affected by these forces?
6. Can you demonstrate forces acting between an electrically charged object and a
magnetic object?
Part 2: Mapping magnetic force fields
Investigative Question: How can we visualize magnetic force fields?
Materials: Various magnets (compasses, bar magnets, ring magnets, neodymium disc
magnets, cow magnets), BBs, iron filings, paper
Procedures:
1. Place a bar magnet underneath a piece of paper. Sprinkle iron filings onto the top
of the paper and look for patterns. Record your observations.
2. Place some compasses on top of the paper (not directly above the magnet, but
near it). Compare the behavior of the compass needle to the behavior of the iron
filings.
3. Clear the iron filings from the paper. Place a second bar magnet beneath the
paper with its end near the end of the first bar magnet. Sprinkle with iron filings
and record your observations. What type of force (attractive or repulsive) is
acting between the two magnets?
4. Repeat step 3, but reverse the position of one of the magnets.
5. Use various magnets (individually or in pairs), paper, and iron filings to map the
fields produced.
6. Use various magnets and BBs to determine the strength of magnetic fields at
different distances and different directions. (Is field strength a vector?)
Demonstration: Mapping the magnetic field surrounding a single wire
conducting a constant (DC) electric current
Observations and Notes:
Part 3: Electromagnets
Investigative Question: What factors determine the strength and direction of the
magnetic field produced by an electromagnet?
Materials: Variable DC power source, insulated wire, nail, staples
Procedures:
1. Coil a wire 40 wraps around a nail. Attach the ends of the wire to the terminals of
the power source. Turn on the power source and touch the end of the nail to a pile
of staples. How many staples can you pick up?
2. Increase the voltage setting on the power source and touch the end of the nail to
the pile of staples. How many staples can you pick up?
3. Wrap a wire 120 wraps around a nail. Attach the ends of the wire to the terminals
of the power source. Turn on the power source with the same settings used in
step 1. How many staples can you pick up?
Part 4: Electric generators
Investigative Question: How can a magnet induce a current in a wire?
Materials: Neodymium magnets, coiled wire, sensitive voltmeter or ammeter
Procedures:
1. Use the coiled wire and nail from part 4. Attach the wire ends to the terminals of
a voltmeter or ammeter.
2. Move the neodymium magnet alongside the coil of wire. Record your
observations of the voltmeter readings.