# An oscillator is producing FM waves of frequency 3KHz with a variation of 9KHz what is the modulating index

$\begin{array}{1 1}(a)\;0.2\\(b)\; 0.3\\(c)\;2\\(d)\;3\end{array}$

Modulation index $m_f=\large\frac{\text{Maximum frequency deviation}}{\text{Modulating frequency}}$
$\Rightarrow \large\frac{9KHz}{3KHz}$
$\Rightarrow 3$
Hence (d) is the correct option.