74 (a) The calculation of the potential at a point near an infinitely long, uniformly charged line was not done in the textbook because it gives an infinite answer when calculated directly from an integration of de/r over the charges.374 (continued)...However, the potential difference between 2 coul/m co two points near such a charged line is finite, and can be calculated, although the calculation involves a couple of b tricks that one often needs to know in problems of this a kind. Let the constant linear charge density be 2, and .B consider two points, A and B, at distances a and b .A respectively, from the line charge as shown. First, consider the line charge to be of finite length, extending from -L to +L on each side of point 0. Calculate V. = 2 In- VL 2 + a2 + 1 the potential at one of the points (say A), and show that the 4TE. plexe VL 2 + a2 - L result is: Now write the expression for VB -VA , and determine its limit as L - . Expand the remaining adt es Idor roots (in the form (1 + a2/L2 and V1 + b2/L to two terms of the binomial theorem, [a/b