Lesson 3.7.5.2

3.7.5.2 Moving charges in a magnetic field Quiz: AQA Physics, Unit 7

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.7.5.2, Moving charges in a magnetic field: 20 multiple choice questions for the AQA Physics (7408), Unit 7: Fields and their consequences (A-level only), written with Revision Ninja.

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The 20 questions

  1. Which equation gives the magnetic force on a charge Q moving at speed v perpendicular to a magnetic field B?

    • F = BQ/v
    • F = BQv
    • F = Bv/Q
    • F = B Q^2 v

  2. A positive charge moves right in a magnetic field pointing into the page. Which direction is the force?

    • Upwards
    • Downwards
    • Into the page
    • Out of page

  3. An electron moves right in a magnetic field pointing into the page. In which direction is the force?

    • Into the page
    • Upwards
    • Out of page
    • Downwards

  4. Why does a magnetic force do no work on a moving charged particle?

    • Force is perpendicular
    • Force is parallel
    • Charge is constant
    • Field is uniform

  5. What is the primary function of the magnetic field in a cyclotron?

    • Deflect into circles
    • Alternate the voltage
    • Increase particle mass
    • Provide linear acceleration

  6. A proton of mass 1.67 x 10^-27 kg moves at 3.0 x 10^6 m/s perpendicular to a field of 0.50 T. What is the radius of its path? Use Q = 1.6 x 10^-19 C.

    • 0.63 cm
    • 2.5 cm
    • 6.3 cm
    • 63 cm

  7. An electron moves at 2.0 x 10^6 m/s perpendicular to a field of 0.10 T. What is the magnetic force on it?

    • 2.0 x 10^-13 N
    • 3.2 x 10^-15 N
    • 3.2 x 10^-14 N
    • 1.6 x 10^-14 N

  8. A charge of 1.6 x 10^-19 C enters a field of 0.30 T at right angles and experiences a force of 2.4 x 10^-15 N. What is its speed?

    • 2.0 x 10^4 m/s
    • 5.0 x 10^3 m/s
    • 5.0 x 10^4 m/s
    • 5.0 x 10^5 m/s

  9. A proton's speed doubles in a fixed magnetic field, perpendicular to its motion. What happens to the radius of its circular path?

    • It quadruples
    • It is unchanged
    • It halves
    • It doubles

  10. For a particle moving at fixed speed perpendicular to a field, the field strength is doubled. What happens to the radius of its path?

    • It doubles
    • It quadruples
    • It is unchanged
    • It halves

  11. An electron and proton enter a magnetic field at equal speeds. Which has a larger orbital radius?

    • Proton
    • Electron
    • Both are equal
    • Neither curves

  12. Which quantity is proportional to speed for a charged particle undergoing circular motion in a magnetic field?

    • Orbital radius
    • Particle charge
    • Cyclotron frequency
    • Orbital period

  13. A charged particle moves in a circle of radius 0.10 m in a field of 0.20 T. Its charge is 1.6 x 10^-19 C and its mass is 9.1 x 10^-31 kg. What is its speed?

    • 3.5 x 10^5 m/s
    • 3.5 x 10^6 m/s
    • 1.8 x 10^7 m/s
    • 7.0 x 10^6 m/s

  14. Which mathematical operation determines the direction of magnetic force on a moving charge?

    • Matrix determinant
    • Vector dot product
    • Vector cross product
    • Scalar addition

  15. An alpha particle of charge 3.2 x 10^-19 C moves at 1.0 x 10^6 m/s perpendicular to a 0.50 T field. What is the force on it?

    • 3.2 x 10^-13 N
    • 1.6 x 10^-19 N
    • 1.6 x 10^-13 N
    • 8.0 x 10^-14 N

  16. What is the angle between the magnetic force on a moving charge and the magnetic field lines?

    • 0 degrees
    • 90 degrees
    • 180 degrees
    • 45 degrees

  17. What is the magnetic force on a charged particle moving parallel to a magnetic field?

    • BQv squared
    • BQv
    • Zero
    • Maximum

  18. An electron moves at 4.0 x 10^6 m/s perpendicular to a 0.020 T field. What is the radius of its path? Use m = 9.1 x 10^-31 kg.

    • 0.11 mm
    • 5.7 mm
    • 1.1 m
    • 1.1 mm

  19. A particle's charge is doubled while its mass and speed are unchanged, in a fixed field perpendicular to its motion. What happens to its radius?

    • It quadruples
    • It doubles
    • It halves
    • It is unchanged

  20. Which factor directly limits the maximum kinetic energy of particles emerging from a cyclotron?

    • Electric potential peak
    • Gap width
    • Frequency of AC
    • Dee radius

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