What would happen if you were to use plastic for a block transformer's core instead of ferrite? And what if you were to do the same with a toroidal core? How would it affect the output voltage and current? And what about a plastic solenoid? All I know is that there would be virtually no inductance in the core.

 

Hi,

Inductance would fall tremendously.
If the core relative permeability was 1000 the inductance would fall by about 1000 times, so if it was a 1mH inductor it would then be about 1uH.

The relative permeability of most plastics that are not magnetically active is around 1 which is the same as air. Thus the core goes to that which matches an air core.

There are some special plastics that may have somewhat higher permeability, but i doubt they would come near the original cores value. Most regular cores have a permeability of at least 50 so even for a low mu core the inductance would drop very significantly. A plastic that had a high concentration of magnetically active particles would be different of course, but that would be a composite core which would contain more than just plastic as its material.