In the book Fundamentals of Physics by Halliday, Resnick and Walker(Extended)(6th edition), in a an ideal transformer it is written that the current induced in the secondary coil induces an opposing emf in the primary coil. Firstly, I want to know how we got this direction of induced emf in the primary coil using Lenz's law.

According to me, the direction of magnetic field in the core due to the first coil should be downwards(assuming that the current is going down the coil). So the magnetic field in the core in contact with the secondary coil is directed upwards. So the direction of current in the secondary coil should be upwards. By similar reasoning the current induced in the primary coil should be downwards. Thus according to me the induced emf does not oppose the current in the primary coil.

Secondly, the book also states that to maintain the emf in the primary circuit, the generator produces an alternating current in the circuit. How does the generator produce this extra current? If this is done by rotating the armature faster, where does the energy required to move the armature faster come from?

All this is taken from Pg 793 under the topic Ideal Transformer, Chapter 33:Electromagnetic induction. Fundamentals of Physics(Extended) by Halliday, Resnick and Walker, 6th edition.(Wiley student edition)


First, you're questioning established, measure facts. But i will clarify.

The electricity runs up the first coil, then down the induced coil. (opposite)

Think of the field between the coils as having 'spark' lines, and know that the side with lowest 'pressure' of electricity will 'attract' electricity from the other, in the opposite direction. Its real simple once you see it.

I'm still learning, although I understand things like oHms law, equilibrium, and electromagnetism a little better than yourself..

Just dedicate lots of time to really understanding the many phenomena, it gets confusing, but keep at itif it's what you really like.



Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.