# The induced current in transformer

1. Nov 21, 2013

Hello, I know that in ideal transformer the law I2/I1 = N1 /N2
I know that I2 is the induced current in the secondary coil, so I1 is the induced current in the primary coil or the current generated from the generator??
where N1 is the number of turns in the primary coil.
and N2 is the number of turns in the secondary coil.

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2. Nov 21, 2013

### Crazymechanic

we don't usually say that current is induced in the primary coil as it is the " driving" coil.The current that runs through it back and forth from a power supply is the reason why a current is induced in the secondary via the core.

In an ideal transformer assuming no losses and a 1:1 turns ratio the secondary current should be just as much as the primary or in other words no energy lost in transformation of voltage/current.

In real life a good designed transformer built from premium quality material can achieve pretty close to ideal some up to 98% efficiency.I think that is as close as you can get to a perfect apparatus.

3. Nov 21, 2013

### rp55

Out of the source (which drives I1's current) there should be a current lag on the voltage if it is via induction i.e. generator source and not corrected via capacitors since voltage lags current. Why isn't this reflected in the formula you present (just a theoretical question give your question)? Opposite of current lag is using capacitors to correct the lag (according to my understanding). Without such correction the "amps" would be affected by such phase anomolies. So for this formula to be correct, there must be a non-inductive (low impedance) source. Am I close there guys?

4. Nov 21, 2013

Ok, but in reality there is an induced current in primary coil since the magnatic field in the primary coil will induce a current in it because there is an alternating current from the source(changing magnetic flux ).
Take for example N1=N2 then I1=I2, I2 is the induced current in the secondary coil and in text books they wright that I1 is the current from the source, but then the induced current in the primary coil will be equal to I1!!

5. Nov 22, 2013

You mean that this formula in ideal transformer does not apply?

6. Nov 22, 2013

### Crazymechanic

the difference is that the primary is directly connected to the source so it acts like one big system starting from the closest transformer down the wires in your house to the transformer primary.
The secondary gets it's voltage induced from the magnetic flux in the core which in turn gets induced from the primary current.

7. Nov 22, 2013

ok, suppose that there is a circuit consisting of a coil connected to a battery, and the coil is in series with a lamp the lamp will delay to shine since phenomena of self electromagnetic induction will happens(you know that the current will increase from zero to I so magnetic flux will increase and emf will be created to oppose the rate of change and so and induced current will be created).
Now in transformer the same thing happens when the alternating source is in the phase of increasing from zero to maximum (in the circuit of primary coil ).
So according to this there is an induced current in the primary.
It is a little bit confusing !!

8. Nov 22, 2013

### Crazymechanic

it's not that the current itself directly opposes itself , it's that as a consequence of a non static amplitude and time varying current induces a non static also amplitude and time varying magnetic field and that field opposes the original current.Also a changing magnetic field induces a current.
Or in this case tried to push back on the original current that created it.

9. Nov 23, 2013