Q 12-08-225JEE MainJEE Main 2017 (2 Apr)Easy
In amplitude modulation, the sinusoidal carrier frequency used is denoted by $\omega_c$ and the signal frequency is denoted by $\omega_m$. The bandwidth $\Delta\omega_m$ of the signal is such that $\Delta\omega_m \ll \omega_c$. Which of the following frequencies is not contained in the modulated wave?
Answer: (B) $\omega_m$
An AM wave $(A_c + A_m\sin\omega_mt)\sin\omega_ct$ expands into
$$A_c\sin\omega_ct + \frac{A_m}{2}\cos(\omega_c - \omega_m)t - \frac{A_m}{2}\cos(\omega_c + \omega_m)t$$
It contains $\omega_c$ and the side bands $\omega_c\pm\omega_m$, but not the signal frequency $\omega_m$ itself.
Solution by Sreeraj P, M.Sc Physics