In amplitude modulation, modulation index 'µ' should be:

The correct answer is Option (1) → µ ≤ 1

The modulation index is the ratio of the amplitude of the signal to that of the carrier, \( \mu = A_m/A_c \). The amplitude of the modulated wave is \( A_c(1+\mu\sin\omega_m t) \).

If \( \mu \gt 1 \), the term \( 1+\mu\sin\omega_m t \) becomes negative during part of the cycle, so the envelope of the wave no longer follows the signal (over-modulation) and the signal is distorted. To avoid this the modulation index is kept less than or equal to 1, \( \mu\le1 \), and \( \mu = 1 \) is 100% modulation.

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):
Amplitude Modulation – “… Here μ = A_m/A_c is the modulation index; in practice, μ is kept ≤ 1 to avoid distortion.”