Hi there- the pictured circuit, taken from Forrest Mims RadioShack electronic lab manual, works as illustrated, but if you take out the capacitor, it does not. I'm trying to get my mind around how this is, but I can't quite see it. Can anyone please illuminate this for me? Thanks!

 

I would imagine that the capacitor needs to charge to a certain level before the "buzzer" will fire. I'm assuming that the buzzer is a piezo type Sonalert. The cap charges, the Sonalert fires, discharging the cap, then the cycle repeats.

 

Thank you for your response. I asked this question elsewhere too. I think part of what I was missing is that the buzzer buzzes at whatever frequency - the tone that sounds continual is the result of thousands of buzzes per second and the discharges you mentioned happen with each buzz. I appreciate the help!