AL a.c. CRO trace

The explanation of the trace based on the physical processes taking place, without using deatiled mathematical analysis, is as follows:
The capacitor discharges through the inductor and resistor. Because of self induction taking place at the inductor, the energy is feeding back into the capacitor, thus an oscillation occurs, which is displayed on the CRO as a sinusoidal trace.
Since the resistor dissipates energy as heat, which is an irreversible process, the amplitude of the trace thus decreases gradually with time.

In fact, when the switch is put to position 2, it will be an electrical LC oscillating circuit, with resistor R be the damping component. Energy will be dissipated through the resistor, so the amplitude of the trace in the CRO decreases.

It is similar to the case in slightly damped simple harmonic motion (damped mechanical oscillation).

In Mathematical method, it is as follows.


圖片參考：http://i601.photobucket.com/albums/tt95/physicsworld9999/physicsworld01May241530.jpg?t=1243150266



2009-05-26 19:18:37 補充：
Just because energy is transferred from the capacitor to the inductor, back to the capacitor, e.t.c. And the current drawn will have energy dissipation through the resistor. That's why the amplitude of the curves decreases.