Tank Circuit Work
consider an ideal capacitor and inductor(no energy is lost) connected in parallel. when a dc source is momentarily placed across the combination,the capacitor is charged while the inductor stores no energy. when the DC SOURCE IS REMOVED, the energy stored in the capacitor transfers to the inductor (creating the positive half cycle of a sine wave). then after all the energy has been transferd to the inductor, the inductor now supplies its energy to the capacitor (the negative half cycle of a sine wave). since the components are ideal, the process goes on continuously. but practical components dissipate energy making the sine wave damped or decrease exponentially to 0.
hope i have explained it clearly