Chapter 22, Problem 9Q

In Example 22–6, it may seem that the electric field calculated is due only to the charge on the wire that is enclosed by the cylinder chosen as our gaussian surface. In fact, the entire charge along the whole length of the wire contributes to the field. Explain how the charge outside the cylindrical gaussian surface of Fig. 22–15 contributes to E at the gaussian surface. [Hint: Compare to what the field would be due to a short wire.]