Switches can be placed anywhere in the circuit but in mains devices the switch is on the live wire, this is for safety reasons. Conductors, insulators and semi-conductors We have already seen that when electrons travel through a material there is resistance to that movement. Only with superconductors is there no resistance and this is a very specialist area - if you want to know more ask me. We can classify most materials into one of three groups depending upon their resistance. Conductors have low resistance, metals are conductors and that is why they are used in electrical wiring.
Semiconductors have moderate resistance and insulators have high resistance.
I say insulators have high resistance - that is not to say they will not conduct electricity but that they are very poor at conducting electricity. Ionic compounds like sodium chloride are poor conductors when solid but good conductors when molten. We are getting into chemistry now which is beyond the scope of these notes, hopefully you will learn these aspects elsewhere or you can check out my networked notes . Perhaps it's best to say that the majority of plastics are very poor conductors but that there are some very special ones that can conduct. In simple terms, if the material allows either electrons or ions to move reasonably freely then the material will conduct.