Amplification is, arguably, the most important contribution of electronics. So important, in fact, that it has had a profound effect on entertainment, radio and TV, and automatic control systems in both home and industry. The implications are far-reaching indeed. Nonetheless, it is as much concept as it is reality.
To the uninitiated, it may seem like the efficiency of amplifiers is more than 100%, where we get something for nothing. This misinterpretation is understandable, because with amplification, we can take the millivolt level signal from, say, a pressure transducer, amplify it electronically, and have enough power in the output to energize the solenoid on a proportional valve. Is this not getting something for nothing? Well, yes and no.
For one thing, the efficiency is not over 100%. Perpetual motion remains beyond the reach of we mere mortals. But it is true that amplification is both real and a matter of interpretation. It’s important enough as a topic to emphasize it a bit more here.