Force from a cone **

(a) A charge q is located at the tip of a hollow cone (such as an ice cream cone without the ice cream) with surface charge density σ . The slant height of the cone is L, and the half-angle at the vertex is θ . What can you say about the force on the charge q due to the cone?

(b) If the top half of the cone is removed and thrown away (see Fig. 1.31), what is the force on the charge q due to the remain- ing part of the cone? For what angle θ is this force maximum?

          Figure 1.31.