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Question:

An amplitude modulated signal is plotted. Which one of the following best describes the given signal?

(1+9sin(2π×104t))sin(2.5π×105t)V

(9+sin(2π×104t))sin(2.5π×105t)V

(9+sin(4π×104t))sin(5π×105t)V

(9+sin(2.5π×105t))sin(2π×104t)V

Solution:

Analysis of graph says
(1)Amplitude varies as 8±1V or 9±1
(2)Two time period as 100µs(signal wave) 8µs(carrier wave)
Hence signal is
[9±1sin(2πt/T1)]sin(2πt/T2) = 9±1sin(2π×104t)sin(2.5π×105t).