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Grade 11 · Science · Physics

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

6 printable versionsBuilding Confidence10 questions · answer keyFree · no account

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Magnetic force on moving charges, and how motors work

Grade 11 Science Worksheet - Building Confidence

NameDate

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

  1. A wire carries 3 A across a 0.5 T magnetic field, with 0.1 m of it in the field. What force acts on it, Ari?

  2. A wire carries 1.5 A across a 0.8 T magnetic field, with 0.4 m of it in the field. What force acts on it, Esme?

  3. Read this first

    Field-line diagram (example data)

    a wire sits between a magnet's north pole on the left and south pole on the right, so the field points to the right. The current in the wire flows out of the page, and a force arrow on the wire points up.

  4. In the diagram, which way does the force on the wire point, Jun?

    • Out of the page
    • To the right, along the field
    • Up

  5. In the diagram, the current is reversed to flow into the page. Which way is the force now, Kira?

    • Still up
    • Down
    • To the left

  6. In the diagram, both the current and the magnet are reversed. Which way is the force, Luz?

    • Down
    • Still up
    • There is no force

  7. In a simple motor, why does the coil turn, Milo?

    • Its two sides are pushed opposite ways
    • Both sides are pushed the same way
    • The magnet spins it by hand

  8. What do the brushes in a simple motor do, Pia?

    • Clean dust off the magnet
    • Slow the coil down
    • Carry current to the coil

  9. What energy change does an electric motor make, Ren?

    • Light to electrical
    • Kinetic to electrical
    • Electrical to kinetic

  10. Why does a running motor get warm, Tala?

    • Magnets give off heat
    • The commutator makes new energy
    • Some energy becomes heat

  11. If the shaft of a small motor is spun by hand, what can the motor do, Zee?

    • Turn into a magnet
    • Make a small current, like a generator
    • Nothing, since it needs a battery
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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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