A1. A plastic rod of length 2L, aligned with the z-axis and centered at the origin, carries a line charge density as given below. In each case, find the leading term in the multipole expansion of \(V(r, \theta)\): (a) $+\lambda$ for whole rod; (b) upper half $+\lambda$, lower half $-\lambda$; (c) upper and lower quarter $-\lambda$, the rest $+\lambda$.