How does a transformer work?

...that's why transformers don't work with direct current.

Simply coils, and when electrical current passes through the primary coil, it creates a magnetic flux that induces a voltage in the secondary coil. If primary has more coils than secondary it's a step down transformer, and if secondary has more coils than primary it's a step up transformer. Power is the same in both coils.
Pin=Pout
P=I*V
So what that tells you is that amperage and voltage are inversely proportional to each other in the two coils.

That's what I know from the top of my head, you can do further reading in a Physics textbook, or google it.

Yes, the flow of electric charge has to be non-direct, or alternating (AC).

Sure. You can also interrupt a direct current to get the same effect. I used to have a Model T ignition with a simple buzzer mounted to the box. Crude, but fun to play with.

There re different type of transformers. for instance distribution transformers are used to distribute electricity and instrument transformers are used for measuring. for more info http://www.esitas.com.tr/en/urunler.aspx

And Asp we might add, the application of DC to the primary will cause a single pulse out of the secondary

Wrong, there is DC half-wave and DC full-wave which would allow ongoing mutual induction,

in fact as long as the DC is changing in magnitude, there would be continuous mutual induction and thus a continuous induced voltage in the secondary.

Also your claim of a " single pulse out of the secondary" even under steady state DC is incomplete as there would be an equal induced voltage upon de-energization,

...and not only that, but due to Lenz's Law there would be a counter-EMF induced in the primary which will oppose the source voltage

Thank you Chum but I'm not sure what you mean by "DC half-wave and DC full-wave"

Quote:

By definition DC need only NOT periodically change polarity, as such the unfiltered output of a rectifier is DC, and if we are talking about an AC sinusoidal single-phase input to a rectifier, then you can either have half-wave DC or full-wave DC as the output.

dalehileman wrote:

That's true, and I apologize if I was misunderstood. Of course if, eg, the source DC V were to increase in amplitude then yes one single continuous sec DC V would result but eventually wouldn't the increasing pri I burn it out

Quote:

Nope, it would not necessarily have to cause an over-current condition, see my examples above as to half-wave DC or full-wave DC or consider a DC sinusoidal input.

dalehileman wrote:

Yes Chum, again, of course there would, but still I don't see how this fact negates my assertion, eg, the immediate effect in practical case of connecting a battery across the primary

Quote:

Because it is not a so-called "immediate effect" due to exactly what I referring to i.e. the time constants and Lenz's Law.

dalehileman wrote:

All bets would be off Chum but it might be interesting to speculate upon the results if the batt internal R and the xfmr sec pri were both to be of zero R

There are super-conductor inductors with massive circulating currents and intense magnetic fields however VAin = VAout + losses would still would hold true, bearing in mind that the losses here would approach if not equal zero. I'm not a physicist, so my knowledge is limited when talking about devices with no resistance, but I can tell you that Ohm's law would mathematically allow infinite current with zero resistance (as long as the voltage was greater than zero), however the limitations of the VA of the supply would prohibit infinite current, even if the entire system had zero resistance, as that would contradict the conservation of energy i.e. "no free lunch".

you can either have half-wave DC or full-wave DC as the output

..or consider a DC sinusoidal input

I'm not a physicist, so my knowledge is limited when talking about devices with no resistance,

but I can tell you that Ohm's law would mathematically allow infinite current with zero resistance

However you cannot have an infinitely increasing magnetic field due to saturation

given that T= L/R and XL = 2pifL, then T is proportional to L and XL is proportional to f

Current lags voltage in an inductor Smile