Question

If any capacitor is open, the ac output voltage wills ____________

(a) Decrease

(b) Increase

(c) Remains the same

(d) Equals zero

I got this question in a job interview.

The origin of the question is Voltage Amplifiers topic in section Differential and Multistage Amplifiers of Electronic Devices & Circuits

Answer 1

Right option is (a) Decrease

To elaborate: Coupling capacitors (or dc blocking capacitors) are use to decouple ac and dc signals so as not to disturb the Q-point of the circuit when ac signals are provided at the input. Bypass capacitors are used to force signal currents around elements by providing a low impedance path at the frequency. The voltage drop across the resistor provides a negative bias to the emitter terminal, thereby reducing its DC gain, while the AC gain will also reduce as the bypass capacitor which was providing low impedance path is left open.