How does the Clapp oscillator work?

[EEMonkey]

I was looking at the Clapp oscillator located here: http://en.wikipedia.org/wiki/Clapp_oscillator
Can someone please explain what the transistor is for? Also, since when the oscillator oscillates, the direction of the current flips...does this have any effect on the battery? Lastly, if you disconnect the power from the oscillator the magnetic field across the inductor collapses quickly. Shouldn't a resistor be used somewhere in order for parts not to be damage? Thanks for the replies in advanced.

 

[Herodotus]

I'm not sure if I am correct because I'm not entirely familiar with Clapp oscillators, but here's my best guess.
The pnp transistor in the Colpitts is used as an amplification device, but I'm not so sure.
Or, it could help with providing the output signal. That's my best answer. The oscillation frequencies can vary with transistor capacitance.
As for your last question...sorry...can't help.

 

[zeitghost]

The transistor provides the gain needed to produce oscillation.

In that diagram, it's shown as a JFET.

The voltage levels across the resonant circuit are unlikely to produce damaging back emfs when the circuit is switched off.

Bear in mind that the circuit does not show any of the d.c. biasing components that are required for a practical device.