Griffith's Figure 2.24

1. Mar 9, 2008

ehrenfest

[SOLVED] Griffith's Figure 2.24

1. The problem statement, all variables and given/known data
This question refers to Griffith's E and M book.

In the paragraph above this figure, Griffith's says that the E-fields cancel in regions i and iii. He does NOT mean cancel completely, correct? That is, the field is NOT 0 in those two regions, correct?

2. Relevant equations

3. The attempt at a solution

2. Mar 9, 2008

kdv

Yes they cancel completely if you assume infinite plates. Of course in real life there are no infinite plates.

3. Mar 9, 2008

ehrenfest

Oh I see. It is because equation 2.17 tells us that the E-field is independent of the distance from the plates.

4. Mar 9, 2008

kdv

Exactly. This is the special property of an infinite surface charge distribution.

A point charge has an E field that goes like 1/r^2. A uniform line of charge (infinite) has an E field going like 1/r. A uniform infinite surface charge distribution has a constant E field