A carrier wave of peak voltage 12 V is used to transmit a message signal. What should be the peak voltage of modulating signal in order to have a modulation index of 75%?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 9 V
The modulation index of an amplitude-modulated wave is the ratio of the peak voltage of the modulating (message) signal to that of the carrier.
\( \displaystyle \mu = \frac{A_m}{A_c} \;\Rightarrow\; A_m = \mu A_c \)
\( A_m = 0.75 \times 12\,\mathrm{V} = 9\,\mathrm{V} \)
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), and it also appears to be out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Exercises – …
