Now separating the vector \(\mathbf{v}\) outside the parentheses into the component \(v \cos\theta\) directed along the vector \(\pmb{\mathscr{E}}\), and two perpendicular components, \(v \sin\theta \...Now separating the vector \(\mathbf{v}\) outside the parentheses into the component \(v \cos\theta\) directed along the vector \(\pmb{\mathscr{E}}\), and two perpendicular components, \(v \sin\theta \cos\varphi\) and \(v\sin\theta \sin\varphi \), we see that the integrals of the last two components over the angle \(\varphi\) give zero.
