Transformer Examples in Physics

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Transformer.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Physics.

Concept Recap

A device that changes the voltage of alternating current by using two coils wound around a shared iron core.

A transformer trades voltage for current (or vice versa) — like a gear system trades speed for torque.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Transformers only work with AC — the changing current in the primary coil creates a changing magnetic flux that induces voltage in the secondary.

Common stuck point: A transformer doesn't create energy — if voltage goes up, current goes down proportionally (power is conserved).

Sense of Study hint: When solving a transformer problem, first identify the primary and secondary coils and their turn counts N_p and N_s. Then use the turns ratio V_s/V_p = N_s/N_p to find the unknown voltage. If asked about current, apply power conservation: V_p I_p = V_s I_s (assuming an ideal transformer).

Worked Examples

Example 1

easy
A step-up transformer has 100 turns on the primary coil and 500 turns on the secondary coil. If the input voltage is 240 \text{ V}, what is the output voltage?

Solution

  1. 1
    Transformer equation: \frac{V_s}{V_p} = \frac{N_s}{N_p}.
  2. 2
    V_s = V_p \times \frac{N_s}{N_p} = 240 \times \frac{500}{100} = 240 \times 5 = 1200 \text{ V}
  3. 3
    The turns ratio is 5:1, so the voltage is stepped up by a factor of 5.

Answer

V_s = 1200 \text{ V}
A transformer changes AC voltage using electromagnetic induction between two coils. A step-up transformer has more secondary turns and increases voltage, while a step-down transformer decreases it.

Example 2

medium
An ideal transformer steps down 11{,}000 \text{ V} to 220 \text{ V}. If the secondary current is 50 \text{ A}, what is the primary current?

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

medium
A phone charger transformer converts 240 \text{ V} AC to 5 \text{ V} AC. If the primary coil has 960 turns, how many turns does the secondary coil have?

Example 2

hard
A transformer with 90\% efficiency steps up 240 \text{ V} to 12{,}000 \text{ V}. If the secondary delivers 2 \text{ A}, what is the primary current and the power wasted as heat?
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Related Concepts

Faraday's LawGenerator

Background Knowledge

These ideas may be useful before you work through the harder examples.

faradays lawgenerator