Question: Coulomb measured the force between two charges by the amount of twist in a fiber from which a small charged pith ball hung at the end of a 10cm long balanced arm, as shown in Fig. 6.6.
a. If q1 = -10pC and q2 = -20pC, what is the electric force between the two "point" charges when the fiber has twisted through 0.2 radians, as shown in Figs. 6.6 and 6.7?
b. How much twist in the fiber will be needed to make the angle between the two lines from the fiber to the two charges become 0.1 radians, as shown in Fig. 6.7?
c. In part (a) what is the magnitude of the electric field produced by q2 at the location of q1?
d. By what factor will the electric field at q1 due to q2 change when the angle goes from 0.2 to 0.1 radians?