Capacitors in common emitter audio amplifier

[nobrainer612]

Homework Statement

Hello. When I looked at my lab manual, I saw the capacitor CB is connected in reversed direction. The AC source is connected to resistor RS, then connected to the negative polarity of CB. But I have no idea why it connects in reverse. Can please anyone tell me the reason? I have tried to connect capacitor in reverse ( not in this audio amplifier) and the capacitor exploded.

 

[NascentOxygen]

The average of the voltage from your signal generator is 0V. The average of the voltage at the junction of R1 and R2 is some positive voltage. Electrolytic capacitors must be connected so average polarity is observed, otherwise they may explode. Instead of maintaining an insulating dielectric, the reversed polarity can destroy part of the dielectric causing a short circuit and high fault current inside the capacitor.