Two small spheres with mass m = 15.0 g are hung by silk threads of length L = 1.20 m from a common point (Fig. 21.44). When the spheres are given equal quantities of negative charge, so that q1 = q2 = q, each thread hangs at θ = 25.0° from the vertical.
(a) Draw a diagram showing the forces on each sphere. Treat the spheres as point charges.
(b) Find the magnitude of q.
(c) Both threads are now shortened to length L = 0.600 m, while the charges q1 and q2 remain unchanged. What new angle will each thread make with the vertical?
(Hint: This part of the problem can be solved numerically by using trial values for θ and adjusting the values of θ until a self-consistent answer is obtained.)