Motors & the Motor Effect · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Motors and the Motor Effect

Science · Forces & Motion · ages 13-14
Name ______________________   Date ____________

  1. In a simple motor, what provides the magnetic field that pushes on the coil?

    • The battery's voltage
    • The magnet around the coil
    • The plastic casing

  2. Inside a simple motor, which part sits between the magnet's poles and spins round?

    • The battery
    • The switch
    • The coil of wire

  3. Which of these has an electric motor inside?

    • A bedside lamp
    • A desk fan
    • A kettle

  4. Which change makes the push on a wire bigger without changing which way it points?

    • Reversing the current
    • Using a stronger magnet
    • Turning the magnet round
    • Swapping the battery leads

  5. A wire feels a force pointing left. You reverse both the current and the magnetic field direction. Which way does the force point now?

    • Still to the left
    • To the right
    • There is no force at all

  6. A wire in a magnet's field is pushed up. Lena reverses the current, then turns the magnet round, then reverses the current back again. Which way is the push now?

    • Up
    • Sideways
    • Down
    • There is no push

  7. Motor A takes in 50 J of electrical energy and gives out 40 J of movement energy. Motor B takes in 50 J and gives out 30 J. All other energy is lost as heat. How many more joules does Motor B waste as heat than Motor A?

    Answer: ______________

  8. A fan motor gives out 45 J of movement energy and wastes 15 J as heat. How much electrical energy did it take in, in joules?

    Answer: ______________

  9. Ben's motor has a tiny current and a weak magnetic field. Keeping the coil's length and position fixed, which pair of changes gives the largest force on its sides?

    • Lower the current and use a weaker magnet
    • Keep the current tiny and paint the coil
    • Raise the current and swap in a stronger magnet

  10. Mia says a loudspeaker makes sound because the magnet vibrates back and forth. Zara says it's the coil that vibrates, pushed by the motor effect. Who is right?

    • Zara
    • Mia
    • Both, the magnet and coil vibrate together
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Answer key

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

Motors and the Motor Effect W1-mt__7BVYUN180-s1

  1. The magnet around the coil · The coil sits between the poles of a magnet, and that magnet's field is what the coil's own field pushes against.
  2. The coil of wire · The coil sits between the magnet's poles, and the motor effect's opposite pushes on its two sides spin it.
  3. A desk fan · A fan's blades have to spin, and a motor is what drives that spin. A lamp and a kettle only need to glow and heat.
  4. Using a stronger magnet · A stronger magnet makes the push bigger. Reversing the current or the field, including swapping the battery leads, flips the push instead.
  5. Still to the left · Reversing the current flips the force once, and reversing the field flips it again, so it ends up pointing the same way it started.
  6. Down · Each reversal flips the push. The two current reversals cancel, and the one field reversal is left, so the push now points down.
  7. 10 · All energy not transferred as movement becomes heat. A wastes 50 - 40 = 10 J; B wastes 50 - 30 = 20 J. B wastes 20 - 10 = 10 J more.
  8. 60 · The energy in equals the useful energy out plus the wasted heat: 45 plus 15 is 60 J.
  9. Raise the current and swap in a stronger magnet · Increasing current and field strength both increase the magnetic force when the coil's length and position are fixed. The pair that increases both gives the largest force among these choices.
  10. Zara · The magnet in a loudspeaker stays fixed. The motor effect pushes the coil, and the coil moves the cone to make sound.
Worksheet · LightMySky