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Magnetic Flux Density (CIE A Level Physics)

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Force on a current-carrying conductor

  • A current-carrying conductor produces its own magnetic field
    • When interacting with an external magnetic field, it will experience a force
  • The force due to a magnetic field can be observed by
    • placing a copper rod in a uniform magnetic field
    • connecting the copper rod to a circuit
  • When current is passed through the copper rod, it experiences a force
    • This causes it to accelerate in the direction of the force

Observing the force on a current-carrying conductor

Copper rod experiment, downloadable AS & A Level Physics revision notes

A copper rod moves within a magnetic field when current is passed through it

Magnetic flux density definition

  • The strength of a magnetic field can be described by the density of its field lines
    • The higher the flux density, the stronger the magnetic field i.e. regions where field lines are closer together
    • The lower the flux density, the weaker the magnetic field i.e. regions where field lines are further apart
  • This is described by the magnetic flux density B of a field, which is defined as:

The force exerted per unit current per unit length on a straight current-carrying conductor placed perpendicular to the magnetic field

  • Magnetic flux density is measured in teslas (T)
  • One tesla, 1 T, is defined as:

The flux density that causes a force of 1 N on a 1 m wire carrying a current of 1 A at right angles to the field

  • To put this into perspective, the Earth's magnetic flux density is around 0.032 mT and an ordinary fridge magnet is around 5 mT

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Ashika

Author: Ashika

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Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.