Q. A small sphere with mass 1.2g hangs by a thread between two parallel vertical plates 5.00cm apart. The plates are insulating and have uniform surface charge densities +σ and -σ . The charge on the sphere is q=9×10-6 What potential difference between the plates will cause the thread to assume an angle of 37° with the vertical as shown in figure?
(a) 30 V
(b) 12 V
(c) 50 V
(d) 25 V
Ans: (c)