Q 12-08-197JEE MainJEE Main 2019 (10 Jan, Shift 2)Medium
The modulation frequency of an AM radio station is $250\ \text{kHz}$, which is $10\%$ of the carrier wave. If another AM station approaches you for license what broadcast frequency will you allot?
Answer: (B) $2000\ \text{kHz}$
Carrier $= \dfrac{250}{0.1} = 2500\ \text{kHz}$, so this station occupies $2500 \pm 250$, i.e. $2250$–$2750\ \text{kHz}$.
A new station with the same $250\ \text{kHz}$ modulation must not overlap this band. At $2000\ \text{kHz}$ it occupies $1750$–$2250\ \text{kHz}$, which does not overlap. $2250$, $2750$ and $2900\ \text{kHz}$ all fall inside or overlap the existing band.
Solution by Sreeraj P, M.Sc Physics