Electromagnetic induction and generators · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Electromagnetic induction and generators

Science · Energy · ages 12-14
Name ______________________   Date ____________

  1. A magnet moves into a coil whose circuit has a gap. The induced voltage must make current flow around the whole circuit.

    Circle one:   True   False

  2. A coil and meter form a closed circuit with no battery. Which action can induce current?

    • Push a magnet into the coil
    • Keep a magnet motionless inside the coil
    • Hold both coil and magnet still together

  3. The coil, magnet and path stay the same. Which change gives a larger induced voltage as the magnet enters the coil?

    • Move the magnet more slowly
    • Move the magnet more quickly
    • Keep the magnet still inside

  4. The chart gives current readings in milliamperes (mA). Field, coil area, motion and total circuit resistance were kept the same. Which coil had the larger reading?

    Few turns2Many turns6
    • The coil with many turns
    • The coil with fewer turns
    • Both coils had equal readings

  5. Zara's bike has a basic bottle dynamo lamp without regulation or stored energy. It is dim while the wheel turns slowly. Which change can brighten it?

    • Keep the wheel turning at its present speed
    • Slow the wheel while keeping it in motion
    • Make the wheel turn faster

  6. A coil stays still in a closed circuit. A nearby electromagnet changes the magnetic field passing through it. Current can be induced without moving the coil.

    Circle one:   True   False

  7. A bike wheel drives a dynamo, and falling water drives a power-station turbine. What do their generators have in common?

    • Both release stored chemical energy from reactions inside their coils.
    • Both supply electricity without receiving any mechanical energy.
    • Both need mechanical input to supply electricity.

  8. Omar says a simple rotating-coil AC generator with slip rings supplies one-way current like a battery. Which statement corrects his claim?

    • Its slip rings swap connections to keep output current one way.
    • Its current reverses each half turn.
    • Its steady rotation stops induction until the coil slows down.
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Answer key

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Electromagnetic induction and generators W1-mt_e0jgUKANT--s1

  1. False · Voltage can be induced, but the gap prevents current from flowing around the whole circuit.
  2. Push a magnet into the coil · Pushing the magnet into the coil changes the field through it. The induced voltage can drive current because the circuit is closed.
  3. Move the magnet more quickly · Quicker movement makes the field through the coil change faster, increasing the induced voltage under these conditions.
  4. The coil with many turns · The many-turn coil reads 6 mA, compared with 2 mA for the few-turn coil. These are supplied results, not a fixed ratio for all coils.
  5. Make the wheel turn faster · The wheel drives the dynamo magnet. Faster rotation can give a larger induced voltage and brighten this basic lamp circuit.
  6. True · The required change is in the field through the coil. Moving the coil is not necessary when an external field changes instead.
  7. Both need mechanical input to supply electricity. · The wheel and turbine supply mechanical input. Turning the generators changes the field through their coils and supplies electricity to connected circuits.
  8. Its current reverses each half turn. · In this AC design, induced voltage reverses each half turn. Slip rings keep each coil end on the same output wire, so the closed-circuit current reverses.
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