Q.Define Modulation index for an AM wave. What is its significance?

The modulation index (or modulation factor) measures how deeply the carrier amplitude is varied by the modulating signal, and it decides whether the modulation is proper or distorted. …

[!TLDR]

Modulation index $m_a = V_m/V_c$; it fixes the depth of modulation and must not exceed 1 to avoid distortion.

The modulation index (modulation factor) of an AM wave is defined as the ratio of the amplitude of the modulating signal to the amplitude of the carrier:

It can also be found from the envelope of the wave as $m_a = \dfrac{V_{max} - V_{min}}{V_{max} + V_{min}}$.

Significance:

• It tells the extent (depth) to which the carrier amplitude is varied by the message. $m_a$ is usually expressed as a percentage (percent modulation).
• For distortion-free modulation $m_a$ must lie between 0 and 1 (0 % to 100 %). If $m_a > 1$ (over-modulation), the envelope is clipped and the recovered message is distorted. …