emf and voltage?

nsaspook said:

This question does highlight a interesting subject of why some students sometimes have problems understanding transformers, motors and generators beyond simple rote formula calculations. Our typical experiences with forces like gravity (conservative), water, pressure combined with water analogies for electricity (voltage) IMO build mental models that tend to blur the distinction between them and non-conservative 'forces' like friction, air resistance and emf (induced and motional in the sense that it cannot be written as the gradient of a scalar field)
Non-conservative fields are 'created' by changing magnetic fields (and magnetic fields with changing electric fields). This is why transformers, motors and generators work and is the basis for countless claims of impossible perpetual motion machines by people who don't see this as a dissipative (mechanical energy is not conserved but lost as heat, etc...) process. It's not the magnetic field that causes charges to move on the secondary circuit loop, it's the induced electric field in the conductor caused by a changing magnetic flux.

This distinction is very important. It's not the way we normally think about voltage and current ...

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