 Besides generators and motors, one other really handy device you can make with induction is the transformer Essentially transformers are just Faraday's original experiment in disguise So you take one solenoid which is just a coil of wire and you pass a current through it And that current is going to make a magnetic field running down there And the advantage of having an also any current is that that magnetic field is also going to be alternating up and down And so you got a changing magnetic field just going to give you a changing magnetic flux And if you have a changing magnetic flux Then you're going to induce an electromagnetic force Voltage in the second coil because the second coil is sharing that magnetic field that make it feels going to come out here And it's going to induce a voltage in that second coil now exactly how you place those coils doesn't matter too much You could have them like that where they're basically in line with each other You could help a little bit by putting a core of iron down the middle So you can have a rod of iron that is shared by the two of them like that And that way the first one will set up a Magnetic field in the iron and then that will be running right down through the second one And that'll help set that changing magnetic field for the second one You can also put them actually completely on top of each other so you can wind them together They have to be electrically separate of course, but you can have the coils around each other Or you can even have them side-by-side Up here like this provided that you get a piece of very magnetic material And join them together like that and then even then the magnetic field generated by this coil Will create a magnetic field that's changing inside that coil and therefore you'll get a voltage So one obvious question to ask is why do people build this because if I could create a potential difference between these two wires here And I wanted to create a potential difference between these two wires Another obvious way of doing that is just to connect the wires directly So I could connect this wire here and that wire there and ignore all that coil stuff So why not do that and the answer lies in here in Faraday's law The electromagnetic force the voltage between those two wires depends on the number of loops in the coil and also when I make my solenoid the strength of the magnetic field in this Solenoid depends on the number of loops in the coil And so if I have a large number of loops in say the first coil and a small number of loops in the second coil That I'm going to be creating a very large magnetic field But I'm going to be producing a relatively small potential on the other one So that allows me to take a very high voltage source and turn it into a low voltage source So that's a very very handy thing when we have 240 volts coming out of the power socket in our houses We rarely want to plug that into a very delicate device that requires a low voltage without first stepping it through a transformer And that's why most power packs and devices have transformers built in Conversely, if you want to make a very large voltage, it turns out that it's much easier to transport electricity long distances Efficiently at high voltage. And so what you want is a step up transformers You want a large number of loops in the second coil and that means that the voltage going out will be much greater than the voltage coming in