Transformers and the National Grid · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Shifting voltage for the long journey

Science · Energy · ages 14-16
Name ______________________   Date ____________

  1. A transformer works on mains AC but does nothing useful with steady direct current.

    Circle one:   True   False

  2. What links the two coils inside a transformer?

    • A changing magnetic field in a shared iron core
    • Wires joining the coils together
    • A battery driving both coils

  3. The secondary coil has twice the turns of the primary. What happens to the voltage?

    • It halves
    • It stays the same
    • It doubles

  4. An ideal transformer doubles the voltage. The primary current is 4 A. What is the secondary current in amps? Type the number.

    Answer: ______________

  5. A transformer has 100 primary turns and 200 secondary turns. The primary voltage is 230 V. What is the secondary voltage? Type the number.

    Answer: ______________

  6. Why does sending power at high voltage cut waste in the cables?

    • High voltage cools the cables as it flows
    • High voltage means low current, and heating grows with current squared
    • Low current needs thicker cables

  7. Power must cross mountains to a far town. Engineers step voltage sky high for the journey, then step it down. Why both steps?

    • Low voltage travels faster over distance
    • Stepping down adds extra power for the town
    • High voltage wastes less on the way, and low voltage is safe to use

  8. A learner connects a transformer to a battery and the output reads zero. What is the mistake?

    • The turns ratio is upside down
    • Steady DC makes a steady field, so nothing is induced
    • The iron core blocks all voltage
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Shifting voltage for the long journey W1-mt_ExV4Kc_7_P-s1

  1. True · Only a changing field induces voltage, and steady DC never changes.
  2. A changing magnetic field in a shared iron core · AC in the first coil makes a changing field that reaches the second.
  3. It doubles · Voltages follow turns, so twice the turns means twice the voltage.
  4. 2 · Power stays constant, so doubling voltage halves the current.
  5. 460 · Double the turns means double the voltage: 230 times 2 is 460.
  6. High voltage means low current, and heating grows with current squared · Low current wastes far less heat, since waste grows with current squared.
  7. High voltage wastes less on the way, and low voltage is safe to use · High voltage keeps the journey cheap, low voltage keeps homes safe.
  8. Steady DC makes a steady field, so nothing is induced · A battery gives steady DC, which cannot induce anything.
Worksheet · LightMySky