In the block diagram of a simple modulator for obtaining an AM signal, identify the boxes A and B. Write their functions.

In the block diagram of modulator A is Square Law Device and B is Band pass filter.
Band pass filter rejects low and high frequencies and allows a band of frequencies to pass through.
Square Law Device is a non linear device. It produces a non linear output of message and carrier signals. The output of square law device
y(t)=Bx(t)+Cx²(t)
Where B and C are constants and
x(t)=message signal(Amsinωmt)+ carrier signal(Acsinωct).