28. Four charges are arranged at the corners of a square ABCD as shown in the figure. The force on the charge kept at the centre o will be: (A) perpend cu ar to side AB (B) along the diagonal BD (C) along the diagonal AC (D) zero 29. An electron travelling in an uniform electric field passes from a region of potential V, to a region of higher potential V, Then (A) Non change takes place in velocity component parallel to interface of two regions. (8) Direction of its motion remains unchanged but speed increases (C) Direction of its motion may change but speed must be decreased. (D) Decrease in kinetic energy is proportional to 3-1, 30. Two equal negative charges - are fixed at point (0, -a) and (0, a) on y-axis. A positive charge Q is released from rest at the point (2a, 0) on the x-axis. The charge Q will: (A) execute simple harmonic motion about the origin (B) move to the origin and remain at rest (C) move to infinity () execute oscillatory but not simple harmonic motion