WHY A STEP-UP TRANSFORMER CANT BE USED AS AN AMPLIFIER?

As you can see in the above figure, for a step-up transformer the amplitude of the output waveform is greater than the input waveform (due to more number of turns on the secondary side of the transformer)

But in the case of the amplifier,

the output voltage the amplifier is also greater than the input voltage.

so there is generally a confusion among most of us that both perform the same operation but in reality its not same operation.

Many of us think that since it is not easy to construct an amplifier.

In the transformer ratio formula, there is an inverse relationship between the current and voltage.

A step-up transformer (Ns>Np) increases the voltage in the secondary coil, at the same time the current in the secondary coil of the transformer gets decreased. (that can be seen by the transformer formula given above)

POWER aT PRIMARY COIL = POWER at SECONDARY COIL 

INPUT POWER =OUTPUT POWER  

(for a Transformer)

But in the case of the Amplifier, there is 

amplification in both the voltage and current

so the 

OUTPUT POWER > INPUT POWER

 so the real amplification is taking place  here