A simple pendulum is set into small-amplitude oscillation. After a few seconds, a horizontal periodic force of the same period as the pendulum is applied at its bob for a short duration and then removed.
(i) State the nature of oscillation of the pendulum before the periodic force was applied.
(ii) How does the amplitude change while the periodic force is acting? Name the phenomenon responsible.
(iii) What type of oscillation will the pendulum exhibit immediately after the driving force is withdrawn?