Chapter 20, Problem 32P

Storm clouds may build up large negative charges near their bottom edges. The earth is a good conductor, so the charge on the cloud attracts an equal and opposite charge on the earth under the cloud. The electric field strength near the earth depends on the shape of the earth's surface, as we can explain with a simple model. The top metal plate in Figure 20.32 has uniformly distributed negative charge. The bottom metal plate, which has a high point, has an equal and opposite charge that is free to move.

Figure P20.32

1. a. Sketch the two plates and the region between them, showing the distribution of positive charge on the bottom plate.
2. b. Complete your diagram by sketching electric field lines between the two plates. Be sure to note the direction of the field. Where is the field strongest?
3. c. Explain why it is more dangerous to be on top of a hill or mountain during a lightning storm than on level ground.