(a) If A and B represent the maximum and ...

CBSE Class 12 Physics 2019 Delhi Set 1 Paper

Question : 24 of 27

Marks: +1, -0

(a) If

A

and

B

represent the maximum and minimum amplitudes of an amplitude modulated wave, write the expression for the modulation index in terms of

A

and

B

(b) A message signal of frequency

20\,\mathrm{kHz}

and peak voltage

10\,\mathrm{V}

is used to modulate a carrier of frequency

2\,\mathrm{MHz}

and peak voltage of

15\,\mathrm{V}

. Calculate the modulation index. Why the modulation index is generally kept less than one?

Solution:

(a) Obtaining the expression for modulation index in terms of

A

and

B

(b) Calculation of

\mu

Reason

We are given that

A = A_c + A_m

\text{ and } B = A_c - A_m

A_c = \frac{A+B}{2}

A_m = \frac{A-B}{2}

\therefore \mu = \frac{A_m}{A_c}

= \frac{A-B}{A+B}

(b) We have

\mu = \frac{A_m}{A_c}

= \frac{10}{15} = \frac{2}{3}

\mu

is kept less than one to avoid distortion.

Go to Question:

Prev Question

Next Question