Q.What is a tank circuit?

A tank (oscillatory) circuit is a circuit that produces electrical oscillations of a desired frequency; in its simplest form it is a capacitor $C$ connected in parallel with an inductor $L$. It is the frequency-determining heart of every LC oscillator.

The oscillation arises from a continual interchange of energy between the two components. Suppose the capacitor is first charged so it stores electrostatic energy. When it discharges through the coil, the changing current induces an emf that (by Lenz's law) opposes the growth of current, so the capacitor does not discharge instantly; instead the current rises gradually and builds a magnetic field around the coil. When the current is maximum the capacitor is fully discharged — all the electrostatic energy has become magnetic energy stored in $L$. The magnetic field then collapses, its induced emf keeps the current flowing in the same direction, and the capacitor recharges with the opposite polarity. The cycle then repeats in reverse, producing an alternating (oscillating) current.

The frequency of these oscillations depends only on the tank elements: …