AP EAPCET 04-Jul-2022 Shift 2 Paper

We know that, Modulation index,
µ=‌

Am

˙Ac

.......(i)
Where, Am= amplitude of message signal
Ac= amplitude of carrier signal
When Am is increased by 1% then, new,
Am′=Am+‌

Am

100

=‌

101Am

100

Similarly, Ac is increased by 3%.
∵ New value of amplitude of carrier wave,
Ac′‌=Ac+3%‌ of ‌Ac
‌=Ac+‌

3Ac

100

‌=‌

103Ac

100

New modulation index;
µ′‌=‌

Am′

Ac′

=‌

101Am∕100

103Ac∕100

‌=‌

101

103

⋅‌

Am

Ac

‌=‌

101

103

µ‌‌‌[From Eq. (i)]
% change in modulation index ‌=‌

µ′−µ

µ

×100
‌=‌

‌ 101 103 µ−µ

µ

×100
‌=−2%