CBSE Class 12-science Answered

Fig (a) represents the unmodulated continuous carrier wave radiation of constant frequency f_c, and constant amplitude V _c .

Fig (b) shows the waveform of the input signal, an audio frequency modulating voltage of frequency f_m and amplitude V_m.  The input signal will, in practice, rarely be a simple pure sine wave, but this form serves to illustrate the concept clearly.

Fig (c) illustrates the waveform of the Radio Frequency (RF) carrier after amplitude modulation by the audio frequency modulating signal.  The outline of the modulated wave (dotted line), known as the modulation envelope, is an exact replica of the modulating signal.