Electricity is supposed to be the "silent servant". So why do transformers hum?
• Transformer hum is caused by a phenomenon known as magnetostriction. To understand why, it is necessary to take a look at how transformers work.
Inside they contain two coils of wire, the primary and the secondary coils, wound onto opposite sides of a ring made out of many thin sheets of iron or some other ferromagnetic material.
An alternating current flowing through the primary coil generates an alternating magnetic field in the iron ring, which in turn creates a voltage in the secondary coil. The ratio of the primary voltage to the secondary voltage is equal to the ratio of the number of turns of wire in the primary coil to the number of turns in the secondary. This allows us to change the hundreds of thousands of volts running through overhead power lines to a ...
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