A carrier wave of peak voltage 14 V is used to transmit a message. What should be the peak voltage of the modulating signal in order to have a modulation index of 70%?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 9.8 V
In amplitude modulation, the modulation index is the ratio of the peak voltage of the modulating (message) signal to the peak voltage of the carrier wave.
\( \displaystyle \mu = \frac{A_m}{A_c} \)
\( \mu = 70\% = 0.7 \)
\( A_c = 14\,\mathrm{V} \)
\( \displaystyle A_m = \mu A_c = 0.7 \times 14\,\mathrm{V} = 9.8\,\mathrm{V} \)
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 – …
