Motors and Generators

The Motors and Generators in the NSW government syllabus is usually answered poorly in Year 12 examinations. What are the reasons for this? Firstly, magnetic fields are abstract things....we cannot see them but we can measure their effects when we do experiments. Secondly, the direction of the magnetic force vector acting on a current carrying conductor is perpendicular to both the magnetic field vector and the current vector and this presents challenges in thinking. Finally, students' exam responses sometimes become confused due to a lack of understanding of the basic terms used in this topic. Here is a list of some of the basic facts in this topic.

  1. Magnetic field and magnetic force are not the same thing.
  2. Current is the rate of flow of charge through a conductor.
  3. Current is measured in ampere (A). Charge is measured in coulomb (C)
  4. The potential difference between two points is the work done in moving a +1 C charge between the points.
  5. Potential difference is measured in volts (V).
  6. Power is the rate at which work is done.
  7. Work is measured in joules (J). Power is measured in watts (W).
  8. Current direction is the opposite to the dirction of electron flow.
  9. A current carrying conductor experiences a magnetic force when it is placed in a magnetic field.

  10. When a conductor moves through a magnetic field a potential difference is induced across the conductor.

  11. When a current carrying conductor is placed in an external magnetic field the interaction of the external magnetic field and the magnetic field of the conductor does not exert a force on the wire.