Cambridge International AS & A Level · 20 · structured
Magnetic field sources and the tesla
Magnetic field sources and the tesla · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- demanding
- Marks
- 7
- Topics
- 3
- Answer
- Complete
A straight conductor can be placed at different angles in a uniform magnetic field. Conventional current is maintained by a low-voltage supply.
- (a)
Explain what a magnetic field is as a field of force and identify two kinds of source, one involving moving charge and one involving a permanent magnet.
2 marks - (b)
Explain why the current-carrying conductor may experience a magnetic force. Compare perpendicular and parallel orientations; do not claim every orientation gives nonzero force.
2 marks - (c)
Define magnetic flux density using the force on a perpendicular current-carrying wire and define one tesla. A 0.080 m wire carrying 2.0 A perpendicular to the field feels 0.048 N; determine B.
3 marks
Ready to self-mark?Reveal the detailed answer guide
(a)
Explain what a magnetic field is as a field of force and identify two kinds of source, one involving moving charge and one involving a permanent magnet.
Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.
- 1
A magnetic field can exert force on a current-carrying conductor, moving charge or magnetic material/dipole.
- 2
It can be produced by electric currents (moving charges) and by permanent magnets.
(b)
Explain why the current-carrying conductor may experience a magnetic force. Compare perpendicular and parallel orientations; do not claim every orientation gives nonzero force.
Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.
- 1
The carriers' magnetic forces are transmitted to the conductor.
- 2
The force depends on orientation: it is maximum when the current is perpendicular to B and zero when parallel in the ideal straight-wire case.
(c)
Define magnetic flux density using the force on a perpendicular current-carrying wire and define one tesla. A 0.080 m wire carrying 2.0 A perpendicular to the field feels 0.048 N; determine B.
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
Magnetic flux density is force per unit current per unit length for a straight conductor perpendicular to the field.
- 2
One tesla gives 1 N per ampere per metre in that orientation.
- 3
B=0.048/(2.0×0.080)=0.30 T.
Complete marking guidance
Use these worked steps alongside the part-by-part answers. They explain the method and mark allocation; they do not add extra marks.
- (a) A magnetic field can exert force on a current-carrying conductor, moving charge or magnetic material/dipole.
- (a) It can be produced by electric currents (moving charges) and by permanent magnets.
- (b) The carriers' magnetic forces are transmitted to the conductor.
- (b) The force depends on orientation: it is maximum when the current is perpendicular to B and zero when parallel in the ideal straight-wire case.
- (c) Magnetic flux density is force per unit current per unit length for a straight conductor perpendicular to the field.
- (c) One tesla gives 1 N per ampere per metre in that orientation.
- (c) B=0.048/(2.0×0.080)=0.30 T.
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