How are electricity and magnetism related?
Materials
For each group
A compass some magnets an arch, made of aluminum foil
Two battery holders and batteries
Wires
Tape thin copper wire of various lengths
A small piece of sandpaper (to take the insulation off of the ends of the wire)
A straw
A nail
Black marking pen bipolar LED motor
Discussion:
> Refer to the first magnetic field diagram you made. Suppose a small bug with a compass starts walking somewhere on the paper with the magnet on it, and keeps walking, always heading in the direction that the compass needle points. Where will the bug end up?
> Suppose you went outside with your compass (but not the magnet) and starting walking always heading in the direction that the compass needle points. Where will you end up?

What to do
1. You can see that a wire with a current in it has effect on a compass by doing a simple experiment shown here. Place a compass on top of a wire, and be ready to connect the wire to a battery so that the electric current can flow in the wire. What happens to the compass? (Don’t do it too long – it’s a short circuit!)
2. Stand up the foil arch and put a stack of magnets under it – as many as will fit. Avoid crinkling the foil, because this would make it stiffer. You can make a current go over the arch by touching the feet with the wires from the batteries. What happens when you start and stop the current?
3. Turn the magnet stack over, and see what effect this has.
4. Reverse the direction of the current, and see what effect this has.
5. In Q1, we found that a wire with a current in it has effect on a compass. In Q2-4, we found that a magnet has an effect on a wire with a current in it. How are these two observations related?
Check #1: How is a wire carrying a current like a magnet, and how is it different?
Please discuss your conclusions with an instructor

6. Obtain 120 cm of thin copper wire. Use sandpaper to scrape the insulation from the last cm (1/2 inch) of each end of the wire. Wrap the wire around a plastic straw, always going around in the same way, and keeping the coil gathered in so that it covers only about 1 cm (1/2 inch) of the straw near one end of it. Leave 12 cm (5 inches) of the wire unwrapped at each end.
Observe the effect of the coil on the compass, when the coil is connected to the batteries and when it is not connected to a battery. (Warning! The wire may get very hot.)
7. Observe what happens when you reverse the batteries, so that current flows the other way in the coil.
8. Observe the directions that the compass needle points in regions near the coil when it is lying on the table. Sketch a magnetic field map for the coil, and compare this to the maps you made with magnets.
9. Is this electromagnet able to pick up a paper clip?
10. Put the nail inside the coil, and observe how the system behaves in various conditions:
Before you turn on the current:
While the current is flowing:
After you disconnect the batteries:
When you reverse the current flow by reversing the batteries:
Is the coil with the nail inside able to pick up a paper clip while it is connected to the batteries?
Check #2: Discuss the electromagnet with an instructor.

Making a motor
A coil of wire becomes an electromagnet when it is carrying a current. Then the coil is attracted to a magnet or repelled by it. If the current is constant, the motion will stop when the magnet and coil get too close or too far away. To keep it turning, we need a switch that turns the current on and off. Here is how to make a motor, in which a turning coil and deliberately dirty contacts make the switch.
Put batteries in a pair of battery holders, and put them in a line so that the positive end of one faces the negative end of the other. Leave a few cm of space between them.
Making the coil
 Obtain a piece of the copper wire that is 50 cm (20 inches) long.
 Remove the insulating paint from the last cm (1/2 inch) of the ends of the wire.
 Wrap the wire around a finger or a thick pencil to make a coil 1 or 2 cm in diameter. You don’t need very many turns.
 At the end, wrap the two ends of the wire around the coil so that it holds together well, and so that the two ends of the wire are sticking out in opposite
 directions.
With the coil laying flat on a surface, use a marking pen to blacken the top sides of the two ends (the sides that are facing you), leaving the bottom sides (that you can't see while the coil is lying on the surface) shiny.
Mount the little coil between the two battery holders, with the ends of the wires through the little holes in the terminals on the battery holders. Check that the coil can turn freely, and that it is reasonably in balance so that it doesn't have a strong tendency to turn to a particular position (you will not be able to make the coil perfectly balanced).
Place a stack of two cylindrical magnets underneath the coil, and connect the free ends of the battery holders with a wire with clips on it. Give the coil a little nudge to get it turning. If the first nudge doesn't work, try to get it turning the other way. If the motor isn't running yet, turn the magnet stack over and try twice more (turning each way). If this still doesn't work, check that the batteries are connected properly, and check the alignment and balance of the coil.
Check #3: Show your motor to an instructor, and explain how it works.

6. Compare the behavior of these two circuits, where we will use only a single battery
(1.5 V) and a bipolar light-emitting diode:
In these diagrams, the switch just means that we don't permanently connect the battery into the circuit -- instead, just touch the battery wire to the other parts, to see what happens when you give the circuit a short jolt or a longer application of the voltage.
Nothing is supposed to happen in the circuit at left -- the voltage is not big enough to operate the LED (but we check, anyway). The circuit at right is more interesting.
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

Compare what happens if you connect the battery for a few seconds to what happens if you just quickly touch the battery wire to the rest of the circuit.
Compare what happens if you remove the nail from the electromagnet.
A motor contains an electromagnet. See what happens if you replace the electromagnet by the motor in the circuit at right, above. There are two things to try: just letting the motor run, or holding the motor shaft so that it cannot turn, as you connect and disconnect the battery.

Each group should hand in one copy of this page
Group:
Names of group members present:
1. Billy claims that all magnets are electromagnets, with the “wires” and the “battery” hidden inside. How would the “wires” have to run, to produce a bar magnet like the ones we have been using? (It might be useful to make a drawing.)
2. If we wrapped two coils the same way around a single straw and had currents going around them in the same direction, would they attract or repel? Explain your answer.

Checks :
A current-carrying wire has a magnetic effect: it causes a nearby compass to point into a different direction. However, the direction of the magnetic field (as indicated by the direction a compass points) is perpendicular to the wire, instead of along it. If the compass needle points to the right when it is on top of the wire, it points to the left when it is underneath it. In fact, the magnetic field points in a circle running around the wire. This means that there isn’t a magnetic pole!
The foil arch moves when you run a current through it. The motion is at right angles to the direction the current is going, and also at right angles to the magnetic field provided by the magnets.
The activity with the compass shows that a current gives a force on a magnet; the activity with the arch shows that a magnet gives a force on a current. According to the
Law of Interaction, the existence of one of these force implies the existence of the other.
Electromagnet
A single wire with a current makes a small magnetic field. Many wires in parallel make a stronger field. That’s what making a coil accomplishes.
The magnetic field map of a long coil resembles that of a bar magnet. The field comes out of one end of the coil and goes in the other. The field then runs down the center of the coil to come back out the other end. The electromagnet doesn’t really have a pole, but you can’t tell it from the outside.
Putting a magnetic material (like a nail) inside the electromagnet makes it stronger. However, the nail remembers a little bit of the magnetism when you turn the current off.\

The electric motor
The flat coil becomes an electromagnet when there is a current going through it. It then resembles a disk magnet with poles just above and below the two flat faces.
The electromagnet turns so that its N pole is facing the S pole of the magnets below the coil. It would then stay there if we didn’t do something. Making the wire partly dirty with the pen makes one side of the wire insulating. When that side of the wire is down, the current is interrupted and there no longer is an electromagnet. But if the coil is turning, it continues to turn – it’s similar to the Law of Inertia. It coasts on around until the clean side of the sire is making contact, which gives the coil andother kick to keep it going.
Many electric motors are similar to this: there is an electromagnet and an ordinary magnet, and some mechanism to turn the current on and off at the right times.