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Grade 11 · Science · Physics

11th grade Magnetic force on moving charges, and how motors work worksheet

6 printable versionsChallenge Me10 questions · answer keyFree · no account

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Magnetic force on moving charges, and how motors work

Grade 11 Science Worksheet - Challenge Me

NameDate

Circle the best answer, or write your answer on the line.

  1. A motor coil has 40 turns, and each side has 0.04 m in a 0.25 T field. It carries 0.5 A. What force acts on one side, Ari?

  2. A motor coil has 25 turns, and each side has 0.03 m in a 0.4 T field. It carries 1.2 A. What force acts on one side, Esme?

  3. A proton moves straight across a magnetic field. What does the field do to its path, Jun?

    • Speeds it up in a straight line
    • Bends it into a curve
    • Leaves it unchanged

  4. A proton sits still in a magnetic field. What magnetic force acts on it, Kira?

    • None
    • A force toward north
    • A force toward south

  5. Milo says a wire lying along magnetic field lines feels the biggest force. Agree or disagree?

    • Disagree: it feels none
    • Agree: the field pushes it along
    • Agree: along the field is strongest

  6. Noah says a current running along a field still gets pushed sideways. Agree or disagree?

    • Agree: any current in a field is pushed
    • Disagree: it must cross the field
    • Agree: fields push along their lines

  7. Pia says a simple motor would spin the same way without its commutator. Agree or disagree?

    • Agree: the magnet keeps it spinning
    • Agree: the commutator is just decoration
    • Disagree: it would rock back and forth

  8. A loudspeaker has a coil attached to a cone, sitting in a magnet's field. What moves the cone, Ren?

    • Heat from the magnet
    • Air pressure from the room
    • Changing current in the coil

  9. What part of an electric fan makes the blades turn, Tala?

    • A motor
    • A light bulb
    • A battery alone

  10. A toy car's motor is wired to its battery the other way round. What happens, Zee?

    • It drives the other way
    • It stops and won't start again
    • It drives faster
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11th grade Magnetic force on moving charges, and how motors work worksheet – printable
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About this worksheet

Magnetic force on moving charges, and how motors work. Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

  • I can find the force on a wire, F = BIL sin θ. It is biggest at 90° to the field and zero along it, and it points at right angles to both the current and the field.
  • I can predict the direction: reversing the current or the field reverses the force, and reversing both keeps it.
  • I can explain a motor: forces push the coil's two sides opposite ways, the commutator flips the current every half turn, and the brushes carry current in. A coil of N turns gives F = NBIL. I know how to make a motor faster.
  • I can describe moving charges in a field: their paths curve, their speed doesn't change, and a still charge feels no force. Loudspeakers, fans and toy cars use these forces.

Standard: none (TX)

Words to know

tesla (T): The unit of magnetic field strength

commutator: A split ring that reverses a motor coil's current every half turn

brushes: Contacts that press on the commutator to carry current in

motor: A device that turns electrical energy into motion using magnetic forces

θ (angle): The angle between the wire and the field lines

Common mistakes

Your child left out the wire's length. The force on a wire is F = BIL: field × current × length in the field.

Your child used cosine. With θ between the wire and the field, the force uses sin θ: none when parallel, most at 90°.

Your child counted one turn. Each of the coil's N turns feels the force, so multiply by N.

Questions parents ask

What is the most common mistake with magnetic force on moving charges, and how motors work?

Your child left out the wire's length. The force on a wire is F = BIL: field × current × length in the field.

Are these 11th grade science worksheets free to print?

Yes. All 6 printable versions at each level are free to print, with the answer key, and no account is needed.

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