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Power transformers are found in every piece of high-end audio equipment you have in your home. Part of our ongoing series on understanding power has to involve the use of transformers, how they work and why they exist. Here's the next part of our continuing story. Thomas Edison's new company, founded to electrify the city of New York, was stumbling on its own technology which was based on DC voltage. It seemed an impossible task to get a steady amount of power to everything connected to it and, in fact, at the time it was indeed impossible for Edison. What was needed was a way to send more voltage than would every be needed down the main wire and then take smaller amounts off the main wire whenever and wherever you wanted. Impossible at the time with DC but quite possible and practical with the same voltage with a slight change to it. If you take a battery and look at it you note it has two ends: a plus and a minus end. Connect a light bulb between the plus and minus and current flows through the light bulb and you get light. This is a simple view of the Edison electrical system. Although he didn't use batteries, his system still had a plus and minus path that ran everything. Nearly 70 years earlier to Edison a fellow named Michael Faraday show the world that if you put a coil of wire across the battery, instead of a light bulb, you create a magnet. And then, in a stunning revelation, he reversed that process and demonstrated that if you move a magnet close to the same coil of wire you create electricity! So electricity and a coil make a magnet and a magnet and a coil make electricity. This discovery changed all of humankind forever and it is the basis of almost all modern technology. Oh yes, there was one last thing he showed people that is quite important to our story. Faraday demonstrated that if a magnet is sitting next to a coil of wire, nothing happens. It is only when that magnet is moving in close proximity to the coil that power flows through the wire. This is really important to our story because 30 years later inventors realized that you didn't need a physical magnet to make this happen. Remember that if you put a coil of wire across a battery you make a magnet? And remember from grade school that a magnet has a plus and a minus (referred to as north and south)? The magnet you make with a coil of wire is either north or south (plus or minus) depending on which way you connect the battery. Now let's put all this together. A magnet moving or changing polarity in close proximity to a coil of wire makes electricity in that same coil - and electricity flowing through a coil of wire makes a magnet out of that same coil - then all you need is two coils of wire close to each other to transfer electricity. One coil is the magnet - the other makes the electricity IF (and this is a big IF) the electricity going to the first coil is changing from plus to minus. If you could swap the battery back and forth across the first coil, say 60 times a second, the energy of the battery would be transfered as if by magic from the battery to the second coil - and all the while the two wires were never touching each other. This is a transformer. Transformers are just two coils of wire: an input coil (called the primary) and an output coil (called the secondary) that are not touching each other but just sit close to each other. Their connection is magnetic only. Moving the battery back and forth 60 times a second is AC - Alternating Current - which simple means DC (Direct Current) Alternating back and fourth between plus and minus. Tomorrow how a transformer changes voltage and then we complete our Tesla Edison story the following day.
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Paul McGowan

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