30. (a) It is clear from symmetry (also from Eq. 22-16) that the field vanishes at the center. (b) The result (E= 0) for points infinitely far away can be reasoned directly from Eq. 22-16 (it goes as 1/z² as z→∞) or by recalling the starting point of its derivation (Eq. 22-11, which makes it clearer that the field strength decreases as 1/r² at distant points).
This is the end of the preview. Sign up
access the rest of the document.