Biot Savart Law and its application part 1

[@davidmusoke]

Good and detailed derivation (thanks!), but you should visually explain, on paper, many of the trigonometric angle properties you quickly do in your head. Very confusing to the 1st time learner wondering how they were derived. E.g., "the lower limit of delta is alpha and the upper one is theta"? or "for infinite wire length L, angle alpha = angle beta" ... Not obvious unless shown on paper. I may know how this came about, but it wasn't that obvious to me anyways.