A transformer is an electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. The electricity that is carried through the power lines are at 400,000 to 750,000 volts, but the voltage that we use at home is typically at 110 to 230 volts. Using the power that came out of the power line would make all the appliances instantly explode. Using a transformer, it can lower the voltage so that it is usable in our homes.

How it works

Inside a transformer there are 2 basic parts to it: the coils, and the iron core. When electricity flows through a coil it produces a magnetic field, and the magnetic field strength is dependent on how large the electric current is. When a magnetic field fluctuates around a piece of wire, it generates an electric current in the wire. So if we put a second coil of wire next to the first one, and send a fluctuating electric current into the first coil, we will create an electric current in the second wire. The current going into the first coil is known as the primary current and the current going into the second coil is known as the secondary current. By putting the two coils of wire next to each other they induce current from one coil to another which is called electromagnetic induction. The electricity doesn’t pass that efficiently through air, so the coils are wrapped around an iron bar instead; the iron bar is known as the core inside a transformer.1When there is power going through the primary coil, the magnetic field is charging. Only when the magnetic field is charging will there be voltage induced in the secondary coil. This means that transformers will only work when it is running on AC (alternating current). AC is always changing constantly and looks like a sine graph. The sine graph is always constantly changing voltage which is constantly causes a change in magnetic field; which means that we are always going to have a voltage induced on the secondary coil.

On DC (Direct Current)


 On AC (Alternating Current)

Transformers are capable of either increasing or decreasing the voltage and current levels of their supply, without modifying its frequency, or the amount of electrical power being transferred from one winding to another. This brings us to the other categories of transformers: Step-up transformers, and Step-down transformers. When a transformer is used to increase the voltage on its secondary winding with respect to the primary, it is called a Step-up transformer. When it is used to decrease the voltage on the secondary winding with respect to the primary it is called a Step-down transformer.

Step-down Transformer


Step-up Transformer

Notice the change in number of winding in the primary coil and the secondary coil


The difference in voltage between the primary and the secondary winding is achieved by changing the number of coil turns in the primary winding (NP) compared to the number of coil turns on the secondary winding (NS). A ratio exists between the number of turns in the primary coil divided by the number of turns of the secondary coil. This ratio is called the ration of transformation or turns ratio (TR). This ratio dictates the operation of the transformer and output voltage coming from the secondary coil.


Transformers are used in your everyday life, this include the power that is going to your house. The electricity from the power station is stepped up so that it can be sent though the power lines to your home, then stepped down to a more usable voltage in your home without blowing up your appliances.


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Electronics/Transformers. (n.d.). Retrieved May 06, 2017, from https://en.wikibooks.org/wiki/Electronics/Transformers