how does a tank circuit (L,C) generate oscillations?

Answer 1

Strictly speaking it doesn't. In order to get steady oscillations you also need an amplifier.

What you probably mean is why an LC circuit can ring for a while with decaying amplitudes?

Because both the inductor and the capacitor are energy storage elements. The inductor stores energy in a magnetic field, the capacitor stores energy in an electric field. By connecting the two you allow the capacitor to feed electrical energy into the magnetic field of the inductor and the inductor can feed energy back into the capacitor. Because the two elements introduce a phase shift of 90 degrees between voltage and current each, the energy continues to oscillate forth and back between the two fields.

But because of the energy conservation and inevitable losses along the way (resistance of wires, mostly), every time the energy changes from one form to another, a fraction is lost as heat and the amplitude of the oscillation decays. If you can add an amplifier into this circuit in such a way that it replaces the lost energy per cycle, the oscillation will continue forever.

Answer 2

First ,

Supply voltage flows through L . Lower Plate of Capacitor gets charged .

then , capacitor tends to Dischargethrough L towards Opposite Polarity plate .

------- If minimum Supply is provided so as to Overcome the Circuit Losses , Oscillations will Exist because of Tank Circuit .

Answer 3

not generate but the tank can control the output of an amplification stage. for example if a 7 mhz signal is input to the amplifier and the tank is tuned to 21 mhz, the output of the amplifier will be the 21 mhz mult of the input..

Answer 4

http://en.wikipedia.org/wiki/LC_circuit