The dance of induction.

(Investigations in magnetism and electric current)

Physics of the Mundane

Adam Johnston

You are supplied with the following:

C  One “antique” ammeter/galvanometer

C  Batteries (D-cells) and battery holder

C  Flexible insulated wire (stripped at ends)

C  Stiff (#22) copper wire with varnish insulation (stripped at ends)

C  Small compass

C  One “disk” or “cow” magnet

1. Mapping the magnetic field of the magnet.

Lay a magnet flat on a piece of blank paper. Using only your compass, map and sketch the lines of magnetic force (known as magnetic field lines) that the magnet creates. In this case, you will need to move the compass to various positions around the magnet to get an impression of these field lines. Label on your drawing the north and south magnetic poles of the magnet. (Your compass= north magnetic pole will be attracted to the magnet=s south magnetic pole, and vice-a-versa.) You should also mark the poles directly on the magnet (with a pencil) so that you can identify them later.

2. Mapping the magnetic field of a wire of current.

Using the battery pack and flexible wire, hook up a circuit, as demonstrated by the instructor.  Do not leave this circuit hooked up for more than three seconds at a time, or else you will drain the battery prematurely.  (You could also burn yourself, as the wires tend to get very hot.)

Allow a line of current to travel in the vertical direction (straight up and down) and use your compass to Afind@ the magnetic field resulting from this moving charge. Sketch out the magnetic field lines on another blank piece of paper. Note that the magnetic field lines should form closed loops. Does your sketch confirm this?

3. Generating electric current.

Use the stiff copper wire to create a coil winding, similar to the instructor=s. This coil should have roughly 20 turns in it, and should be just big enough so that your magnet can fit through it. Hook each end of this coil to the ammeter and note the reading on the ammeter.

Using your disk magnet, devise a way to produce a current in the coil of wire. You will sense this current by noting the motion of the needle on your ammeter.

What does the magnet have to be doing in order for a current to be created? How many different variations can you add to this method? (i.e.: Does the magnet have to be pointed the same way? Does it have to move the same way?) How do these different variations affect the direction of the current?  What way does the magnet need to be oriented in order to produce the most current?