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What is Electrical transformer?

A device that converts AC voltages by electromagnetic induction between two or more windings on a core. In an ideal transformer the voltage is proportional to the number of turns (V1/V2 = N1/N2) and the current inversely proportional to it, so the power on the primary and secondary sides is equal. For example, applying 100 V to a transformer with a turns ratio of 10:1 gives 10 V on the secondary, and drawing 5 A from the secondary makes the primary current 0.5 A. It can isolate the input from the output electrically, and switching power supplies make it small by operating it at high frequency. It cannot convert DC voltages.

Read the beginner explainer: AC vs DC Explained: Impedance, Phase and Power Factor

Japanese name: 変圧器

Electrical transformer appears in 3 practice questions across 2 topics, including Circuit and electromagnetism basics, Power Electronics Circuits.

Field: Power Electronics Circuits

Try it: questions about Electrical transformer

An AC voltage of 100 V (RMS) is applied to the primary of an ideal transformer with 1000 primary turns and 100 secondary turns. What is the secondary voltage (RMS)?

  1. A1000 V
  2. B100 V
  3. C10 V
Show answer and explanation

Answer: C. 10 V

In an ideal transformer, voltage is proportional to the number of turns: V2 = V1 × N2/N1 = 100 V × 100/1000 = 10 V. Because power is conserved, current is inversely proportional to turns, so the secondary current is ten times the primary current. A transformer transfers voltage through a changing magnetic flux, so it cannot convert DC voltages.

An 8 Ω resistive load is connected to the secondary of an ideal transformer with turns ratio N1:N2 = 10:1. What impedance is seen from the primary side?

  1. A800 Ω
  2. B80 Ω
  3. C0.8 Ω
Show answer and explanation

Answer: A. 800 Ω

In an ideal transformer the primary voltage is n = N1/N2 times the secondary voltage and the primary current is 1/n times the secondary current, so the impedance seen at the primary, V1/I1, is n² times the secondary's V2/I2: 10² × 8 Ω = 800 Ω. Because of this impedance transformation, transformers are also used for impedance matching, for example between an amplifier and a loudspeaker.

Electrical transformer in the explanations

Questions that mention Electrical transformer (3)

  1. An AC voltage of 100 V (RMS) is applied to the primary of an ideal transformer with 1000 primary turns and 100 secondary turns. What is the secondary voltage (RMS)?
  2. An 8 Ω resistive load is connected to the secondary of an ideal transformer with turns ratio N1:N2 = 10:1. What impedance is seen from the primary side?
  3. When an ideal transformer converts the primary voltage into a lower secondary voltage, which of the following correctly describes the relationship between the primary and secondary currents?

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