Two thin rods of length L lie along the x-axis, one between x=a/2 and x=a/2+L and the other between x= - a/2 and x= - a/2 - L. Each rod has positive charge Q distributed uniformly along its length.
1)Assuming a >> L, find the magnitude of this force reduces to. (Hint: Use the expansion ln(1+z)= z - z^2/2+z^3/3 - ...), valid for |z| <<1. Carry all expansions to at least order L^2/a^2.)
2) What does the result of 1) mean?