I'll try to help you out.. sorry it has been confusing. I have a good understanding of this but a hard time explaining - which might show not such a strength over this concept after all.. lol

Milsk might be able to help out with his physics, but I'll try.

When S3 is closed you have parallel components, right?

From Ohm's law we know that voltage is the same across each branch. If R1, R2 and R3 were not present the voltage of the battery would be equal to the voltage drop across R6, and consequently, equal to the voltage of the capacitor. They are all branches in a parallel form, hence they all have the same voltage.

However, on this diagram, R1, R2 and R3 are present but the principle holds. The voltage will be the same for each branch in parallel. The way I think of it (Idk how scientifically that it) is that the battery is supplying a certain voltage, but there is a voltage drop (taking away) over R1, R2, and R3. Thus, the total voltage will be the voltage provided by the battery, minus the voltage drops over R1, R2, and R3. Thus, the voltage drop across R6 and Capacitor will be the V from battery minus the voltage drop over R1 R2 and R3. Although the battery gives a higher voltage the resistors besides it will take some "voltage away".

While when S3 is closed, all the components are in series. The resistors will only delay the charging process of the capacitor, but it will not change the capacitor's voltage.

I hope it helps some.. feel free to say you're still confused. it took me a while to figure this out...