Answer – 9V
Explanation –
We are given –
Amplitude of carrier wave ; \[{{A}_{c}}\] = 12 V
Modulation index (m) = 75% = 0.75
Amplitude of the modulating wave = ${{A}_{m}}$
We will now use the formula of modulation index, given by –
$$ m=\frac{{{A}_{m}}}{{{A}_{c}}} $$
$$ \therefore {{A}_{m}}=m{{A}_{c}} $$
$$ {{A}_{m}}=0.75\times 12 $$
$$ {{A}_{m}}=9V $$
Therefore, 9V should be the peak voltage of the modulating signal in order to have a modulation index of 75%.