(a) Define linear charge density and state its SI unit.
(b) A thin straight rod of length L carries a total charge Q distributed uniformly along its length. Write an expression for the elemental charge dq located at a distance x from one end of the rod when the rod is taken as the x-axis.
(c) A point charge q is placed on the axis of this rod at a distance a from its nearer end. Explain, without performing any calculation, why the electrostatic force on q must be obtained through an integration rather than by simple algebraic addition of forces from individual charge elements.