What is the modulation index of an over modulated wave?
(a) Zero
(b) 1
(c) >1
(d) <1

Hint: There are three types of wave i.e. modulated, under modulated and over modulated wave. By remembering and understanding what modulation index and its effect on the wave is, we can get our modulation index of an over modulated wave.

Complete step-by-step answer:
A carrier wave, after being modulated if the modulated level is calculated then such answer obtained is known as modulation index or modulation depth. It states the level of modulation that a carrier wave undergoes.
$\mu $ denotes the modulation index or modulation depth. It is generally denoted in percentage. Also denoted by m.

The above figure is the perfect modulated wave. So, the modulation index of this waver will be 100%. So, modulation index $m = 1$
Now, we will see an under-modulated wave: Figure of this wave is as shown below.

Here, the modulation index of the under modulated wave is 0.5 which is less than 1. So, written as $m < 1$.
Now, taking over modulated wave:

This is wave 1. Now showing wave 2, we get

Combining both the waves, we get this:

Here, the modulation index of over modulated waves is 0.5 which is less than 1. So, written as $m > 1$ .
Thus, option (c) is the correct answer.

Note: Don’t get confused in under modulated waves and over modulated waves as both are having minor differences in graphs. So, be careful while selecting the modulation index answer and remember the graph as it is easy to solve.