Believe it or not, you could never own and use your hard drive if society had not invented and made use of the transformer. Transformers work when you’re dealing in the realms of AC or alternating current, the kind of current generally used by power plants to create and distribute electrical energy. Let’s take a closer look.
Transformers work in conjunction with the concept of mutual induction, which states that two or more coils of wire can be placed in such a way that changing the magnetic field created by one induces a voltage in the other. That means if you have two mutually inductive coils and one is energized with AC, an AC voltage will be created in the other coil. The device by which this is done is called a transformer.
Transformers are used not only to create voltage in new coils but to adjust the voltage in the second coil in whatever way is convenient. The voltage produced in the secondary coil is always equal to the AC voltage across the powered coil multiplied by the ratio of secondary coil turns to primary coil turns. If the secondary coil is powering a load (like a light or a motor), the current through the secondary coil will be the opposite and the primary coil current multiplied by the ratio of the primary to secondary turns will apply. Often this process is explained with a mechanical analogy in which torque and speed are meant to represent voltage and current, respectively:
Imagine that a transformer is to coils with different currents and voltages as a geartrain is to gears of different sizes moving at different speeds. Speed multiplication gear trains steps torque down and speed up. Step-down transformers step voltage down and current up.
This might be a good time to be reminded of the difference between voltage and current. Voltage is the difference in charge between two points. Current is the rate at which charge is flowing. If charge were water, voltage would be the water pressure and current would be the rate at which the water flowed.
Transformers can step only AC voltage up or down; the process doesn’t work with direct currents. If you’re trying to transmit electrical power over long distances, it’s much more efficient to do so with stepped-up voltages and stepped-down currents because you can use smaller-diameter wire with less resistive power losses. That’s why alternating current is almost always used by power providers for easier shipping to industry, business, or private consumer use.
That means that the factory that made your hard drive used AC power that was able to be carried to the facility through use of a transformer. The same goes for the electricity that you use to run your computer in the first place. Without transformers, your hard drive would cease to be.