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20. Magnetic fields

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  1. 20.1 Concept of a magnetic field

    1. • understand that a magnetic field is an example of a field of force produced either by moving charges or by permanent magnets

    2. • represent a magnetic field by field lines

  2. 20.2 Force on a current-carrying conductor

    1. • understand that a force might act on a current-carrying conductor placed in a magnetic field

    2. • recall and use the equation F = BIL sin θ, with directions as interpreted by Fleming’s left-hand rule

    3. • define magnetic flux density as the force acting per unit current per unit length on a wire placed at right-angles to the magnetic field

  3. 20.3 Force on a moving charge

    1. 20.3.1The direction of the force on a charge moving in a magnetic field

      • determine the direction of the force on a charge moving in a magnetic field

    2. 20.3.2F = BQv sin θ

      • recall and use F = BQv sin θ

    3. 20.3.3The origin of the Hall voltage and derive and use the expression V H = BI /

      • understand the origin of the Hall voltage and derive and use the expression V H = BI / (ntq), where t = thickness

    4. 20.3.4The use of a Hall probe to measure magnetic flux density

      • understand the use of a Hall probe to measure magnetic flux density

    5. 20.3.5The motion of a charged particle moving in a uniform magnetic field

      • describe the motion of a charged particle moving in a uniform magnetic field perpendicular to the direction of motion of the particle

    6. 20.3.6How electric and magnetic fields can be used in velocity selection

      • explain how electric and magnetic fields can be used in velocity selection

  4. 20.4 Magnetic fields due to currents

    1. • sketch magnetic field patterns due to the currents in a long straight wire, a flat circular coil and a long solenoid

    2. • understand that the magnetic field due to the current in a solenoid is increased by a ferrous core

    3. • explain the origin of the forces between current-carrying conductors and determine the direction of the forces

  5. 20.5 Electromagnetic induction

    1. • define magnetic flux as the product of the magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density

    2. • recall and use Φ = BA

    3. • understand and use the concept of magnetic flux linkage

    4. • understand and explain experiments that demonstrate: • that a changing magnetic flux can induce an e.m.f. in a circuit • that the induced e.m.f. is in such a direction • As to oppose the change producing it • the factors affecting the magnitude of the induced e.m.f.

    5. • recall and use Faraday’s and Lenz’s laws of electromagnetic induction