GCSE Science
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Transformers change the potential difference of electricity. There are two main types of transformer that are used in the national grid. These are step up and step down transformers. Each of them consists of a two coils of wires around an iron core. In a step up transformer, the voltage is increased and the primary coil has fewer turns of the wire than the secondary coil. In a step down transformer, the voltage is decreased and the primary coil has more turns that the secondary coil.
The way it works is by electromagnetic induction, and it only works with an a.c. current. The current passes into the primary coil, which produces an alternating magnetic field in the iron core. The magnetic field is constantly changing direction 100 times per second if the frequency of the a.c. current is 50Hz. This alternating magnetic field induces a potential difference across the secondary coil at the same frequency as the primary coil. Depending on whether it is a step up or step down transformer, the potential difference will be greater or lower across the secondary coil compared to the primary.
There is a formula you can use to work out what the potential difference across the coils will be. It is p.d across primary coil/p.d across secondary coil = number of turns on primary coil/ number of turns on secondary coil. For example, a transformer has 100 turns on the primary coil and 2000 turns on the secondary. If the input p.d. is 500V, then the output p.d. can be calculated by rearranging the formula to give 10000V.
Transformers are almost 100% efficient so we can assume that the power that goes into them also comes out. This gives us another handy formula, which is, the current in the primary coil x the p.d across it = the current in the second coil x the p.d. across it. For example, the current of 2A is supplied to the primary coil of a transformer with a p.d. of 300V across it. The secondary coil has a 15A current flowing though it. By rearranging the equation we can work out the p.d. across the secondary coil as being 40V.
There is another type of transformer called a switch mode transformer. These are the ones you get in your laptop and mobile phone chargers. They operate at very high frequencies between 50 and 200 kHz. They also use very little power when your laptop or mobile phone is not plugged in. Which is good for when you accidentally leave your charger in the socket.
References:
1. [ Ссылка ]
2. CGP GCSE Physics AQA Revision Guide.
