relays

That is true. A transistor base (a lump of doped silicon) in and of itself has no gain either. It's only when assembled into the more complex "mechanism" we call a transistor that the device exhibits gain. It's just that we tend to think of the transistor taken as a whole as being a circuit element, and tend to ignore the fact that it is really a composite "machine". The power that ends up in the load originates in the external power supply, not the transistor.

Take the relay example. It employs an electromagnet to actuate a switch comprised of a spring-loaded lever with contacts. A small amount of electric power for the magnet can control a much larger amount of electric power via the contacts. If you change the magnet for a handle, you can control a large amount of electrical power with a small amount of mechanical power.

the first electrical one

before (artificial) electricity there were mechanical gain devices like capstans (the tension on the rope is multiplied by the modulus of friction and some (exponential?) expression involving the number of turns)

but the first device with gain was probably the goad applied to a beast of burden

bye.

does that mean a mosfet is not an amplifier either?

once the gate is charged it stays on...

bye.

The *first* gain element was the rudder. Plane surfice on the end of a lever using water flow to permit one man to turn many tons of ship. You can call that hydraulic if you like :-)

Those don't have power gain, and cannot be configured to self oscillate. It's like a transformer or a lever, not like a transistor, relay or vacuum tube.

That *does* have power gain, and could be configured to self oscillate.

I think that there were single-celled organisms before the first multicellular life that had power gain, but I need to think of a mechanism that would cause them to self-oscillate.

I nearly lost my coffee when I saw what actually appears to be a carbon amplifier offered for sale over 100 years after their first commercial application.

For completeness, there is a very nice page about the hitoric ones here:

--- OK.

Pout dB = 10 (log10) ------ Pin

Where Pout is the power dissipated in the load and the relay contacts, Pin is the power needed to latch the contacts, and dB is the power gain in decibels.

Clearly, no matter how minute the amount of power dissipated by the coil while latching the relay, or how great the power dissipated by the load and contacts after having been latched, unless Pin is zero the power gain can never be infinite.

JF

On a sunny day (Fri, 14 Nov 2008 07:50:33 -0600) it happened John Fields wrote in :

mm If the Po is infinite, then infinity / something = infinite

Well, they reproduce. Maybe a sort of oscillation. This is getting pretty esoteric..

You left out time.

John

But that water will come out forever, with no further effort exerted on the valve. The longer you wait, the more output power, without limit. The output power is the *integral* of the input power.

John

Many of the other examples that have been tossed around here show a basic misundersanding of what power gain is, and the latter part of the above seems at first to be more of the same (give me a place to stand and a long enough lever, and I can move the earth with one finger, but that's not power gain but rather a transformation of a small force over a large distance to a large force over a small distance). Thinking about it futher, I can't shake the feeling that the rudder is somehow modulating the power from the propeller or sails and thus has power gain. Then I start to think that it only points the the power from the propeller or sails in another direction and thus doesn't have power gain. And I can't think of a mechanism that will prove without any doubt that there is power gain - a feedback oscillator. I am going to thow this one out as a question;

All this discussion has implied we're getting something for nothing. Energy is still conserved, no matter how fast the hand waves ;-)

...Jim Thompson

And rightly so. He was quite clear in defining power gain and not energy gain.

"POWER: The time rate at which work is done or energy emitted or transferred"

Source:

"Power is the time rate at which work is done or energy is transferred. In calculus terms, power is the derivative of work with respect to time."

Source:

"Physicists have specific definitions for 'energy' and 'power' even though these words are often used interchangeably in common speech. Energy is the ability to do work, while power is the rate at which work is done."

Source:

Indeed. What is called a gain element is something that controls a larger thing with a smaller thing, where 'thing' is usually assumed to be interpreted in terms of power of one form or another. We also have a tendency tend to think in analog terms, where there is a continuous functional relationship between the input power and the controlled power, but this is not a necessary requirement.

A transistor doesn't *produce* power from nothing. It modulates the power available from the power supply.

There you go ;-)

...Jim Thompson

We use a cute little latching relay that will pull in in 500 usec, using about 125 microjoules, just once. After it's pullec in, it will easily dump 50 watts, which is 50 joules per second. Measured over one second, its power gain is 400,000. Over one year, it's 1.3e13. There's no limit on the power gain if you're patient enough.

John