Lesson 3.7.5.1

3.7.5.1 Magnetic flux density Quiz: AQA Physics, Unit 7

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.7.5.1, Magnetic flux density: 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 force on a straight current-carrying wire placed at right angles to a magnetic field?

    • F = Bl/I
    • F = B/(Il)
    • F = BI/l
    • F = BIl

  2. Which rule gives the direction of the force on a current-carrying conductor in a magnetic field?

    • Fleming's left-hand rule: thumb for force, first finger for field, second finger for current
    • The right-hand grip rule: thumb for current, fingers curling in the direction of the field
    • Lenz's rule: induced current always opposes the change that produces it
    • Fleming's right-hand rule: thumb for motion, first finger for field, second finger for induced current

  3. How is one tesla defined?

    • The flux density that gives a force of 1 N on a 1 m length of wire carrying 1 A parallel to the field
    • The flux density that gives a force of 1 N on a 1 m length of wire carrying 1 A at right angles to the field
    • The flux density that gives a force of 1 N on a 1 m length of wire carrying 1 mA at right angles to the field
    • The flux density that gives a force of 1 N on a 1 cm length of wire carrying 1 A at right angles to the field

  4. A wire of length 0.25 m carries 2.0 A at right angles to a field of flux density 0.25 T. What is the force?

    • 0.25 N
    • 1.3 N
    • 0.13 N
    • 0.017 N

  5. A wire of length 0.40 m carries 5.0 A at right angles to a field and experiences a force of 0.080 N. What is the flux density?

    • 0.0040 T
    • 0.040 T
    • 2.5 T
    • 0.10 T

  6. A wire carries current parallel to a uniform magnetic field. What is the magnetic force on the wire?

    • BIl multiplied by the square root of 2
    • zero
    • half of BIl
    • maximum, equal to BIl

  7. A wire carries a current northwards and the magnetic field points eastwards and is horizontal. In which direction does the force act?

    • northwards
    • eastwards
    • vertically upwards
    • vertically downwards

  8. In a top-pan balance experiment, a wire carrying current in a magnetic field pushes down on the pan and the reading rises by 0.020 kg. Taking g = 9.8 N/kg, what is the force on the wire?

    • 0.020 N
    • 0.0020 N
    • 2.0 N
    • 0.20 N

  9. A wire of length 0.050 m carries 3.0 A at right angles to a field. The force is 0.060 N. What is the flux density?

    • 4.0 T
    • 0.90 T
    • 0.40 T
    • 0.0040 T

  10. A straight wire of length 0.10 m carries 4.0 A at right angles to a field and experiences 0.12 N. What is the flux density?

    • 3.3 T
    • 0.48 T
    • 0.30 T
    • 0.0048 T

  11. A graph of force against current for a wire at right angles to a fixed field is a straight line through the origin with gradient 0.030 N/A. The wire is 0.20 m long. What is the flux density?

    • 6.7 T
    • 0.15 T
    • 0.030 T
    • 0.0060 T

  12. A wire in a magnetic field experiences no force. Which explanation is most likely?

    • The wire is parallel to the field lines, so no component of the field is perpendicular to the current
    • The field is too weak to exert any force on a wire at all
    • The wire is perpendicular to the field, so the forces on each end cancel
    • The current is so large that the forces on its two halves cancel out

  13. The current and the field are both doubled for a wire at right angles to the field. By what factor does the force change?

    • unchanged
    • 2 times
    • 4 times
    • 8 times

  14. A wire of length 0.15 m carries 2.5 A at right angles to a field and experiences a force of 0.10 N. What is the flux density?

    • 0.040 T
    • 0.27 T
    • 2.7 T
    • 0.67 T

  15. What are the SI base units of the tesla?

    • kg s^-2 A^-1
    • kg m^2 s^-2 A^-1
    • kg s^-1 A^-1
    • kg m s^-2 A^-1

  16. A wire in a uniform field has force 0.36 N when B = 0.60 T and I = 3.0 A, with the wire at right angles. What is its length?

    • 0.20 m
    • 0.40 m
    • 0.072 m
    • 1.8 m

  17. A current flows to the right across the page and the magnetic field points into the page. Which way does the force act?

    • into the page
    • upward, in the plane of the page
    • out of the page
    • downward, in the plane of the page

  18. A wire of length 0.25 m carries 0.80 A at right angles to a field and experiences a force of 0.060 N. What is the flux density?

    • 3.3 T
    • 0.030 T
    • 0.19 T
    • 0.30 T

  19. A wire carries 1.5 A and is 0.20 m long at right angles to a field. The force is 0.45 N. What is the flux density?

    • 1.5 T
    • 0.68 T
    • 0.14 T
    • 6.8 T

  20. Which change would double the force on a wire at right angles to a fixed magnetic field?

    • Doubling either the current in the wire or the length of wire lying in the field
    • Doubling the separation between the magnet poles
    • Halving the current in the wire
    • Turning the wire so it is parallel to the field lines

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