When is a transformer supplied with electricity?

Big Bang 3, textbook

75 23.5 Direct and alternating current transformer crash course You will hear a lot more about the transformer next year. Transformers consist of an iron core and two coils (B 23.32), ie coiled wires. The alternating current in the first coil generates a magnetic field in the iron core, and this in turn generates an alternating current in the second coil. If the second coil has fewer turns, the voltage is lower there. For example, you can step down from 230V to 5V and charge your cell phone or electric toothbrush (B 23.33). With a transformer, a little electrical energy is always lost as heat, and you can feel this when you touch the charger (A23). You use these things all the time in everyday life, for example when charging electrical devices (1 info: transformer crash course). In the household, the voltages are always transformed down, because many devices require less than 230V. There are also cases in which it is transformed upwards, for example to transmit the current via high-voltage lines. When using high voltages there is much less heat loss and much thinner cables can be used. If the overhead lines had 230V instead of 380,000V, the cables would have to have a cross-section of 100m 2 (A22)! This saving in cables was an important reason why alternating current finally prevailed over direct current in the power grid (1 Info: The current war). The current war In everyday life, electricity played almost no role until around 1880. But then Thomas Alva Edison (B 19.12, p. 31) invented a very durable light bulb that soon replaced gas lamps. He wanted to supply the USA with the electricity it needed, but had a major competitor in the engineer and industrialist George Westinghouse. Edison used direct current, Westinghouse used alternating current. This was followed by a long and bitter dispute that is now known as the "current war". Edison wasn't squeamish about it. Many cats and dogs and even an elephant were killed with alternating current on his behalf to show how dangerous it was. Nevertheless, it could not prevent the victory of alternating current because it can be transported over long distances (B 23.35). With alternating current, the electrons do not flow in one direction, but they swing back and forth. On average, the voltage in the household is 230V. Alternating current has the advantage that transformers can be used to easily change the voltage and adapt it to the respective requirements. B 23.32 Left: An electric toothbrush has one coil in the handle and the second in the charging station. Right: An open cell phone charger: The transformer (arrow) is wrapped in yellow insulating tape. The transformer always makes a charger a little richer (A23). B 23.33 Fat transformers generate high voltage for overhead lines. B 23.34 Starting in 1896, generators sent alternating current from the Niagara Falls over 40 kilometers of copper wire to Buffalo. That would have been impossible with direct current. B 23.35 For testing purposes only - property of the publisher öbv

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