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Magnetic Fields

Magnetic flux density

  • 3 things to know
  • Unit A2 2

Overview

Recall questions on the definition as force per unit current per unit length, the equation and the unit, the definition of the tesla and its base units, typical values for a laboratory magnet and for the Earth, worked calculations of flux density and current, why only the length inside the field counts, and the force against current graph.

What you need to know

Answer each one before you reveal it.

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Key term

Give the equation that defines magnetic flux density

Key term

State the unit of magnetic flux density.

Key term

Express the tesla in base units.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Define magnetic flux density.

    Model answer

    Magnetic flux density is the force acting per unit current per unit length on a conductor placed at right angles to the field.

  2. 2

    Give the equation that expresses that definition.

    Model answer

    B = F/(Il), where B is in tesla, F the force in newtons, I the current in amperes and l the length in metres.

  3. 3

    State the unit of magnetic flux density.

    Model answer

    The tesla, T.

  4. 4

    Define the tesla.

    Model answer

    One tesla is the flux density that produces a force of one newton on each metre of a conductor carrying one ampere at right angles to the field.

  5. 5

    Express the tesla in base units.

    Model answer

    A tesla is N A⁻¹ m⁻¹, which in base units is kg s⁻² A⁻¹.

  6. 6

    Is magnetic flux density a vector or a scalar?

    Model answer

    A vector, since the field has a direction as well as a magnitude.

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