Question

what is amplitude modulation

Answer 1

Amplitude modulation is change in the amplitude of a wave to get the required result. Here a is the amplitude and change in amplitude has been done as a' is smaller then a.

Answer 2

Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. In amplitude modulation, the amplitude (signal strength) of the carrier wave is varied in proportion to that of the message signal being transmitted. The message signal is, for example, a function of the sound to be reproduced by a loudspeaker, or the light intensity of pixels of a television screen. This technique contrasts with frequency modulation, in which the frequency of the carrier signal is varied, and phase modulation, in which its phase is varied.  

AM was the earliest modulation method used for transmitting audio in radio broadcasting. It was developed during the first quarter of the 20th century beginning with Roberto Landell de Moura and Reginald Fessenden's radiotelephone experiments in 1900.This original AM is sometimes now called double-sideband amplitude modulation (DSB-AM) to distinguish it from more sophisticated amplitude modulation methods. AM remains in use today in many forms of communication; for example, it is used in portable two-way radios, VHF aircraft radio, citizens band radio, and in computer modems in the form of QAM.