Magnetic Flux Density

Test yourself

Magnetic Force on a Wire Experiment

We can investigate how the force on a wire varies with flux density, current and length of wire in the magnetic field, by using a top pan balance.

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  • Set up the apparatus as shown in the diagram.
  • For this investigation, aim to make the angle of the wire with the field as close as possible to 90°.
  • Caution: the current should not exceed 4A (as the variable resistor is likely to smoke).
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Variables to investigate

  • Using the arrangement on the previous slide, we can investigate the magnitude of the force as a function of:
    • Flux density of the magnetic field
    • Current in the wire
    • Length of wire in the field
    • Angle between wire and field lines
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  • The formula for the magnetic force is:
    • F=BILsinθF = BIL\sin \theta
  • Where F is the force, B is the magnetic flux density, L is the length of wire in the field and θ is the angle between the field lines and the wire.
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Example analysis

  • An example of the analysis possible:
    • Plot a graph of force against current.
    • The line of best fit should be a straight line that passes through the origin.
    • By comparison with “y = mx + c”, the gradient of the line should be equal to BLsinθ.

Jump to other topics

1Measurements & Errors

2Particles & Radiation


4Mechanics & Materials


6Further Mechanics & Thermal Physics (A2 only)

7Fields & Their Consequences (A2 only)

8Nuclear Physics (A2 only)

9Option: Astrophysics (A2 only)

10Option: Medical Physics (A2 only)

11Option: Engineering Physics (A2 only)

12Option: Turning Points in Physics (A2 only)

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