A massless rod of length L has two equal charges (q) tied to its ends. The rod is free to rotate in horizontal plane about a vertical axis passing through a point at a distance `(L)/(4)` from one of its ends. A uniform horizontal electric field (E) exists in the region. (a) Draw diagrams showing the stable and unstable equilibrium positions of the rod in the field. (b) Calculate the change in electric potential energy of the rod when it is rotated by an angle `Deltatheta` from its stable equilibrium position. (c) Calculate the time period of small oscillations of the rod about its stable equilibrium position. Take the mass of each charge to be m.

Answer

(b). `DeltaU=(EqL)/(2)(1-cosDeltatheta)`
(c) `T=pisqrt((5mL)/(Eq))`