# Why does a transformer require AC to generate electromagnetic induction?

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And I mean what is happening on an atomic level that is not happening with DC so that induction can occur? I’ve been doing a lot of reading to wrap my head around it but I can’t seem to get an answer that explains what is happening throughly, just a lot of “just because”. What is going on with the electrons that allows them to transfer over to the second coil that does not occur with DC?

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Let’s skip the primary side of the transformer and just look at the secondary side first.

It is a change in the magnetic field that creates a current in a wire. So for induction york, you need a magnetic field that changes over time.

If a constant magnetic field could create a current then just putting a magnetic net to a wire would result in a current constant current. That does not occur. You do get a current when you place or remove the magnets but not when it is stationary.

So to create a current you can have a moving magnet for example a spinning magnet beside a coil, The rotation will change the magnetic field and create a current that changes over time depending on how fast the magnetic field changes. This is how generators work and what they produce is AC.

Then a look at the primary side.

A current through a wire creates a magnetic field around the wire so we can use that phenomenon. To get a changing magnetic field you need a changing current through the wire, that is AC.

Put that next to a magnet that can rotate and you have created an electric motor.

All electric motors require AC in the coils. A DC motor uses a commutator to make a switch that changes how the wires are connected to the cold and create AC. It is like if you connect a battery to a child and then physically rotate the battery so its connections are reversed.

If you put the two coils together one creates a changing magnetic field. The other will create a charging current from the changing magnetic field.

Current creates a magnetic field. Constant current creates a constant magnetic field. Changing currents create a changing magnetic field.

Constant magnetic fields don’t create current. Changing magnetic fields do create currents

If you apply DC to the primary side of a transformer the current will ramp up in the primary side and will increase the magnetic field in the core and the change in the field creates a voltage on the secondary which pushes current along. Then the magnetic core saturates, the field is no longer changing so there’s no voltage/current on the output, and there’s no inductance to resist current on the primary so it’s just a giant resistor an promptly lights on fire

For AC the current is constantly increasing and decreasing so you stay in that starting time frame so if passes energy across during all of its operation

It’s important to not that electrons aren’t transferring, their energy is.

Think of a transformer like a seesaw. If you hook one end(secondary) up to and old timey water pump then just place a big rock on the other side (DC) then you just get one pump and nothing interesting happens. If you instead get your friend to grab the end of the seesaw and push it up and down repeatedly then the pump will work

We’re using the magnetic field as the board on the seesaw to transfer the energy from the changing electric field on one side into a changing electric field on the other side

Electrons do NOT move from the the primary to the secondary (unless you are talking about an autotransformer). There are in fact transformations intended to solely provide power to the secondary without a galvanic (wire) connection (isolation transformers). Transformers connect circuits through magnetic and not electric coupling.

A constant current generates a constant magnetic field. DC by definition has a constant voltage which will produce a constant current. It should be noted that a DC circuit will not always have a constant voltage or current, but the frequency content is usually not very high for most linear circuits.

In the simple transformer the primary is coils of wire wrapped around one side of an iron loop. Closely coiled wire is what is known as a solenoid, and generates a relatively constant magnetic field on the interior of the loop whose strength is proportional to the current flowing in the wire.

The secondary is another solenoid wrapped around the opposite side of the iron loop. Since both wires are insulated there is no direct galvanic (electrical) connection between the two solenoids.

With AC, the current flowing through the primary generates a magnetic field that varies with the varying current. Iron (and other ferrous materials) operate as a kind of wire for magnetic fields. The changing magnetic field originating from the primary travels through the iron core and through the secondary coil. Just as a changing current creates a changing magnetic field, a changing magnetic field will induce a current to flow. Thus a changing current is created in the secondary.

Since DC does not have a changing current it cannot create a changing magnetic field and thus a transformer will not work with a typical DC circuit. It should be noted that the iron core is not strictly necessary, and they do make air core transformers, but the iron core greatly increases the magnetic coupling between the primary and secondary.