The point of this experiment is to show you the relationship
between **voltage** and the **electric field**.
You will make measurements of the voltage at a number of
points in a pan of water, and then use those measurements
to calculate the electric field between the points.

There is a useful analogy which may help you to understand the connection between voltage and electric field.

On a topographic map In your experiment today ---------------------------------------------------------------- (x, y) position is shown | (x, y) position is shown | | contour lines indicate | contour lines indicate ALTITUDE | VOLTAGE | | calculate the SLOPE of ground | calculate the ELECTRIC FIELD like so: | like so: | change in altitude | change in voltage slope = ----------------- | E field = ----------------- change in position | change in position | | (meters) | (volts) = ----------------- | = ----------------- (meters) | (meters) |

On a topographic map, slope is the **derivative** of altitude,
with respect to position.
On the map of your experiment, the electric field is the **derivative**
of voltage with respect to position.

- Does altitude have a direction?
- Does slope (of the ground) have a direction?
- Does voltage have a direction?
- Does electric field have a direction?

Here's an example of a topographic map: a section of the 7.5-minute series around Phoenicia, New York. The contour lines are at 20-foot intervals. Click on the map to see the full-size version.

Copyright © Michael Richmond. This work is licensed under a Creative Commons License.