what is modulation?what is amplitude modulation?

Answer 1

Modulation is a method of packing information signal bounded by an envelope of the carrier signal. We can have amplitude modulation, frequency modulation, phase modulation, pulse width modulation and so on (see ref. 1). The ref 2 has an AM circuit.

AM signal can be expressed as

S(t) = A(1+Bsin(ws t)) cos(wm t) where
A- amplitude of the modulating signal
B – amplitude of the modulated signal
ws – signal frequency
wm – modulating wave frequency