transformers

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8 Terms

1
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What is a transformer?

A transformer is an electrical device that changes the voltage of an alternating current (AC) using electromagnetic induction.

2
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How does a transformer change voltage?

  1. An alternating current (AC) flows through the primary coil, creating a changing magnetic field.

  2. This magnetic field passes through the iron core to the secondary coil.

  3. The changing magnetic field induces a voltage in the secondary coil (by the generator effect).

  4. If the secondary coil is part of a closed circuit, an AC current flows.

(This only works with AC because a changing magnetic field is needed to induce a current)

3
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What does the iron core do in a transformer?

The iron core strengthens and channels the magnetic field between the coils, ensuring efficient energy transfer.

4
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What is the difference between step-up and step-down transformers?

  • Step-up transformers: Increase voltage (more turns on secondary coil).

  • Step-down transformers: Decrease voltage (fewer turns on secondary coil).

(Used in the National Grid to reduce energy loss in power transmission.)

5
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What is the transformer equation?

Vs/Vp = Ns/Np

Where:

  • Vₛ = Voltage in secondary coil (V)

  • Vₚ = Voltage in primary coil (V)

  • Nₛ = Number of turns in secondary coil

  • Nₚ = Number of turns in primary coil

(The ratio of voltages equals the ratio of turns.)

6
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What equation links power in an ideal transformer?

Vp​Ip​=Vs​Is​

Where:

  • Vₚ & Iₚ = Voltage and current in primary coil

  • Vₛ & Iₛ = Voltage and current in secondary coil

(In an ideal transformer, power is conserved: power in = power out.)

7
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Why are step-up and step-down transformers used in the National Grid?

  • Step-up transformers increase voltage to reduce current.

  • Lower current means less energy lost as heat in power lines.

  • Step-down transformers reduce voltage for safe home use (230V in the UK).

8
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Why do transformers only work with AC and not DC?

  • AC constantly changes direction, creating a changing magnetic field.

  • A changing field is needed to induce voltage in the secondary coil.

  • DC (direct current) does not change direction, so no voltage is induced.