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Transformers - explanation

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Explain what a transformer is, why it is not 100% efficient and state its uses in real life.

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TRANSFORMERS
Transformers can increase the voltage and reduce the current of an oscillating signal or vice versa, by having two coils of wire wrapped around a single core.

The general principle involves Faraday's Law which states that the rate of change of flux linked to a coil is equal to the emf induced. Hence if we have an oscillating voltage in a primary coil we generate lines of flux which can then be linked into a secondary coil, producing a voltage. The amount of flux linkage is determined by the number of turns on each coil, the size of the magnetic field and the area of the coil. Here we are only varying the number of turns on each coil, N1 and N2, and therefore the ratio of the voltages is given by V2/V1 = N1/N2.

This is strictly only true for an ideal transformer, where ...

Solution Summary

Transformers can increase the voltage and reduce the current of an oscillating signal or vice versa, by having two coils of wire wrapped around a single core.

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True and False Questions about Transformers

A transformer is an electrical device that can change the voltage from one value to another, based on the principle of Faraday's Law of Induction. Consider a transformer with Np turns of wire in the primary (input) circuit and Ns turns in the secondary (output). Which of the following statements are true? Briefly justify your answers.

1. Transformers can only work with DC voltages (not AC).

2. If the secondary voltage is lower than the primary voltage, then the secondary current is also lower than the primary current.

3. To have a higher voltage on the secondary, Ns < Np.

4. Transformers in your neighborhood step up the voltage from power plants so that there is plenty of electricity to run your many home appliances.

5. If Ns > Np, the average power in the secondary is greater than the average power in the primary.

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