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Force Fields

This is the second half of the force field experiment. The electric field lines will be mapped indirectly by first determining the equipotential lines. A galvanometer will be used as a detector. When no current flows between two probe points (zero deflection on the galvanometer), then there is no potential difference between the points, then the two points are on an equipotential.

MATERIALS

Electric Field

Mapping Board and probe / 3 Conducting plates
Connecting wires / galvanometer
Power supply / paper
Template / tape

Mapping board:

The electric field mapping board consists of a flat board on which is placed a sheet of carbonized conducting plate to be attached at the bottom of the plate. Mapping is done on a piece of paper that is placed on top of the mapping board.

Here’s a diagram of the top of the mapping board that will be used in this experiment.

The two contact points on the sides will be connected to the power supply. The holes are like grid lines that divide your conducting plate (which will be attached to the bottom – with charge configuration facing outward) into grid lines of different potentials. (In other words, if I applied a potential difference of 6 V from the power supply, and there are 6 holes, the first hole will be 1 V higher than the negative terminal of the power supply, the second hole will be 2 V higher, and so on.)

PROCEDURE:

1. Attach the one conducting plate at the bottom of the mapping board through the two screws at the bottom (remember, the charge configuration should be facing outward).

2. Use the diagram below to connect all the components.

3. Attach a piece of paper on top of the mapping board by pushing the board and inserting the corners of the paper to the 4 black paper guides. In order for the paper to stay in place, tape the paper on the board.

4. Attach the template corresponding to the charge configuration on the conducting plate to the guides on the mapping board and trace the diagram. You now have a picture of the configuration you are mapping on your paper. Then remove the template.

5. Insert the U-probe between the mapping board with the arm with a hole on the paper and the arm with the bolt in contact with the conducting plate at the bottom.

6. Turn on the power supply and set the voltage output to 3 V. Move the probe until the galvanometer shows zero deflection. Mark the point on the paper by inserting a pencil through the hole. Locate a series of 8 to 10 points of the same potential. Draw a dashed-line curve through these points on the paper.

7. Move the wire connected to the next hole on the mapping board (This corresponds to the next grid line.) Locate another series of equipotential points. Continue this procedure until you have moved the wire to all the holes on the mapping board.

8. Repeat the procedure for two other conducting plates.

* Make copies for each member of the group.

9. On your own copy, draw curve lines perpendicular to the equipotential lines to represent the electric field lines. Do not forget to indicate the field direction.

These are the different charge configurations that will be mapped in this experiment:

QUESTIONS:

1. Directions of the fields are indicated on the field lines. Why are there no directions indicated on equipotential lines?

2. Examine the result obtained in the second plate. In what region does the electric field have the greatest intensity? Explain why you know that from your map, and justify.

3. Examine the result obtained in the parallel plates. Comment on the result of the field lines (a) between the plates and (b) near the edge of the plates.

4. Compare the magnetic field lines obtained for the horseshoe magnet and the third plate (Faraday’s pail). Are there any similarities? differences?

5. In conclusion, what are the similarities and differences between magnetic fields and electric fields?