Q. Explain the frequency response curve of a  RC coupled amplifier

The frequency response curve of a typical RC coupled Amplifier is shown below:

In mid frequency range(50 Hz to 20KHz),the voltage gain of the amplifier is constant, as is from the analysis. With the increase in the frequency in this range, the reactance of the coupling capacitor Cc reduces thereby increasing the gain but at the same time lower capacitive reactance causes higher loading resulting in lower voltage gain. Thus the two effects cancel each other and uniform gain is obtained in mid frequency range.

At low frequency range(below 50 Hz), higher capacitive reactance of coupling capacitor Cc allows very small part of signal to pass from one stage to the next and also because of higher reactance of emitter bypass capacitor CE, allows very small part of signal to pass from one stage to the next and also because of higher reactance of emitter bypass capacitor CE, the emitter resistor RE is not effectively shunted. Thus the voltage gain falls off at low frequencies.