Why is AM modulation not an efficient way of modulation?

Answer 1

-- The power output stage in the transmitter must be operated either class A or

class B. Whereas in FM the power output stage in the transmitter can operate class C

which uses much less power per watt delivered to the antenna.

-- For full modulation, audio power is required equal to 1/2 of the RF power of the

transmitter output stage.

-- At full modulation, 2/3 of the total power arriving at the receiver is at the carrier

frequency, which conveys none of the information.

-- A receiver designed for AM reception is susceptible to a wide variety of natural

and man-made noise.