Physics help please:Explain the mechanism by which AC (alternating current) through the primary circuit of a transformer produces an alternating voltage and current in the secondary coil. Then explain why this would or would not work with DC (nonalternating current) in the primary coil.

Question

egenriether · Answer

Ok, as in the other post the same rules apply.  Now instead of having a single winding around a core you have two windings around the same core.  Just as before you will make a changing magnetic field in the core, but this time (AC) it will continue to change, not reach saturation.  Therefore an EMF will develop in the second winding by Faraday's Law.  Why?  Because the magnetic field you make in the core will contribute to a changing magnetic flux through the secondary winding.  The voltage induced is by the same mechanism that caused the eddy currents in the single winding core, only this time they're not just going around in circles in the core, they are also going around in a secondary circuit.  Let me know what you don't follow from my explanation, there is a lot to take in here...

anonymous · Answer

Oh my goodness, I am so sorry I do not understand that at all. I am going to read it again slower.

anonymous · Answer

What is saturation?

egenriether · Answer

When current is passed through a coil it makes a magnetic field.  This magnetic field aligns the atoms in the metal core, which serves to amplify the field.  Without the core the magnetic field would be in air which is about the same strength it would be in vacuum.  The core helps because as its atom's magnetic fields align with the coils field they add together and the field is much stronger.  It amplifies the field.  However at some point you will have aligned all of these atoms that your field is capable of aligning.  At that point no more increase is seen and the field stops growing.  This happens pretty quick, but with an AC source the current reverses direction before that happens and the atoms start to turn the other way and the process repeats.  This is why a DC transformer would not work.  The field changes at first but then all of the atoms are aligned and the field stops growing.

egenriether · Answer

I am making a drawing of transformers for you...

anonymous · Answer

okay @egenriether

egenriether · Answer

Ok, I tried to be clear.  Let me know your questions!

anonymous · Answer

Thank you so much! and i will!

egenriether · Answer

Note in the drawing I did not say the field in the core must be changing (growing or shrinking) in time.  That is Faraday's Law, That is why we need AC to make the transformer work.  I left that point out of the writing...

anonymous · Answer

okay it makes sense, but if it had a DC not an AC how would it affect this system?

anonymous · Answer

would it affect the current flow? and not allow the process to start over in the opposite direction?

anonymous · Answer

@egenriether

egenriether · Answer

Yes that is right, the DC would be good for a short time, as the field builds.  Then after the field got as big as it could the changing stops and the transformer stops working.

anonymous · Answer

okay thank you soooo much! i really appreciate your help!

egenriether · Answer

No problem.  Its fun!

anonymous · Answer

Okay I posted one more question. Do you think you could help me with it?