TO THE STUDENT

You may be part of a group for the first part of this exercise. If you are, the group should carry out the experiment and collect the data together, but each student must record the data in his or her own booklet. Be sure to record the data exactly as you observe them. After the data have been collected, each student should answer the questions independently.

After you have finished the experiment and have recorded all of the data, you will be asked to answer some questions about the experiment and the data you recorded. Your answers must be written in the space provided. Make sure that you understand each question before you begin to write. At any time while you are writing your answers, you may look back at the directions for the experiment and the data you collected. Be sure that your answers are written as clearly and neatly as possible.

Before you begin the exercise, read the list of materials given below and check to make sure that your group has everything listed.

• compass
• cardboard tube (e.g. from roll of toilet paper)
• bottom from cardboard box
• one length of 22 gauge insulated magnetic wire marked galvanometer, the wire should have alligator clips on its ends.
• one length of 22 gauge insulated magnetic wire marked generator, the wire should have alligator clips on its ends.
• strong bar magnet with its north pole marked N
• tape

(Caution: Keep the compass needle and your digital watch away from the magnet.)

The generation of electricity involves changing energy from one form to another. For example, coal contains chemical energy. Burning coal turns some of coal's chemical energy into heat energy. In a power plant, the heat energy from burning coal is used to turn water into steam and to give the steam mechanical energy. The mechanical energy of the steam is used to turn coils of conducting wire inside a magnetic field. Because the coils of wire are turning inside a magnetic field, the mechanical energy of the turning coils is converted into electrical energy in the wire, producing an electrical current in the wire.

In this event you will make a simple generator, consisting of a magnet and wire that is wrapped around a cardboard tube. Using the generator and a galvanometer, a device that can be used to measure small amounts of current, you will study the conversion of mechanical energy into electrical energy. (Note: the compass will be used to detect the presence of an electric current.)

To make the galvanometer:

Fold the flaps of the cardboard box as shown in Figure A below.

Wrap the box with the magnet wire marked galvanometer. Leave about 15 cm of unwrapped wire at each end, as shown in Figures B and C below.

Place the compass in the wrapped cardboard box.

To make the generator:

Wrap 50 turns of the wire marked generator around the cardboard tube. Leave at least 15 cm of extra wire at each end, as shown in Figure D below.

Using the alligator clips as shown in Figure E, clip one end of the galvanometer wire to one end of the generator wire. Clip the other end of the galvanometer wire to the other end of the generator wire.

Observations

Before each of the following trials, separate the magnet and the galvanometer by several meters, and orient the galvanometer so that the compass needle points due north. Then, during each trial, note the direction and the amount (in degrees) of the needle's deflection (west of north or east of north) as the tip of the magnet enters or leaves the tube. As the amount of current flowing in the wire increases, the amount of deflection will increase. For example, figure F illustrates a deflection of 45 degrees east of north.

After each trial, record your observations in the Data Table on the following page.

For trials 1-3, place the tip of the North pole of the magnet just inside the cardboard tube. The tube should be held still during trials 1-3.

Trial 1. Hold the magnet still with the tip just inside the tube.

Trial 2. Move the magnet slowly toward the tube as shown in Figure G; when the tip of the magnet is just inside the tube, stop. Then move the magnet slowly away from the tube and, when the magnet is 2 meters away from the tube, stop.

Trial 3. Move the magnet rapidly toward the tube; when the tip of the magnet is just inside the tube, stop. Then move the magnet rapidly away from the tube and, when the magnet is 2 meters away from the tube, stop.

For trials 4-6, place the South pole of the magnet inside the same end of the tube as before. The tube should be held still during trials 4-6.

Trial 4. Hold the magnet still with the tip just inside the tube.

Trial 5. Move the magnet slowly toward the tube until the tip of the magnet is just inside the tube, stop. Then move the magnet away from the tube and stop as in step 2.

Trial 6. Move the magnet rapidly toward the tube until the tip of the magnet is just inside the tube and stop. Then move the magnet rapidly away from the tube and stop as in step 3.

Questions

Please answer the following questions by yourself.

1. Based on your results, describe the relationship between: (a) how fast you moved the magnet and the amount of current that flowed in the wire; and (b) the pole of the magnet (north or south) that was inside the tube and the direction of the compass's deflection.
   
   

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2. You live along a moving river, and you have a wire, a paddle wheel, and a bar magnet. Describe how you could use these materials to produce an electrical current. Include a diagram of your setup in your description.
   

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