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Physics · Grades 10–12

Ideal transformers and conservation

Use turns ratios and distinguish the ideal AC model from real losses.

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Learn the idea

Changing flux

A transformer uses changing magnetic flux linking coils. The simple steady ratio model assumes alternating operation.

Voltage ratio

Secondary-to-primary voltage ratio equals the corresponding turns ratio in the ideal model.

Power

An ideal transformer conserves input and output power; a step-up voltage does not multiply power without an input.

Real systems

Real devices have losses, insulation limits and safety requirements. All exercises here are theoretical.

Worked examples

An ideal transformer has 200 primary turns and 600 secondary turns. Primary voltage is 4 V. Find secondary voltage.

Vs = VpNs/Np = 4 × 600/200 = 12 V.

12 V

A step-up transformer increases which ideal output quantity?

An ideal transformer changes voltage/current ratio, not creates power.

Voltage

Check your understanding

  1. An ideal input is 10 V at 2 A. Output voltage is 5 V. Find output current.

  2. What is required for normal transformer action?

    1. Changing linked magnetic flux
    2. No magnetic coupling
    3. A permanently unchanging flux only

  3. Why is a voltage increase not a claim that energy has been created?

Answers and marking notes

Answers and marking notes
  1. 4 A

    Input power is 20 W; output current is 20/5 = 4 A.

  2. Changing linked magnetic flux

    Induced emf requires time-varying flux.

  3. In the ideal model current decreases correspondingly at the same power.

    Credit conservation and the current-voltage tradeoff.

Further reading and review references

These are reference links, not copied exercises, institutional endorsement or proof of independent review.

Independent educational review required. Grade bands are approximate; these are not officially aligned curricula.