ELECTRIC MOTORS AND ELECTROMAGNETIC INDUCTION
2 marks · NormalExplain why a wire carrying a current experiences a force when placed at right angles to a uniform magnetic field.
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Must show: Overlap of magnetic fields, Difference in field strengths causes a force
Also accept: Appropriate description using field patterns
Common mistakes: Not mentioning overlapping fields; Stating 'because there is a current' without explaining mechanism
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Mentions overlapping of magnetic field due to current with the external field.
M1 · 1 mark · States that the force results from stronger and weaker field regions on different sides of the wire.
Worked solution
The current in the wire produces its own magnetic field. When placed in an external magnetic field, these fields overlap. One side of the wire has fields reinforcing (stronger), and the other has fields opposing (weaker). This difference causes a force that pushes the wire from the stronger to the weaker field region.