Archive for February 24th, 2008


Basically, all of the electrical power in your home is first passed through a series of transformers. So how exactly do they work?

Transformers reduce current before transmitting electrical energy over very, very long distances through wires. By reducing current, the voltage is increased, making for a very economical transmission of power. An alternating current in the primary coil changes the magnetic field strength which induces a voltage in the secondary coil.


City power lines usually operate at 15,000 V. But before the electricity enters a house, the potential difference is reduced to 120 V. The change in the potential differences depends on the turns ratio. If the number of loops on the secondary coil is decreased, the potential difference on that side decreases (this would be a step-down transformer.) With Faraday’s law, we can derive the equation for the turn ratio.

ΔV1/ΔV2 = N1/N2

Energy is, of course, sadly dissipated in a transformer but it is one of the most efficient of electrical machines! In fact, large transformers can perform at efficiencies that are around 95%.  Wow!


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