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.

The Value of Physics

For a moment, let us put to one side the value of Physics as a science in its own right that describes the natural world. By studying Physics we pick up skills that flow over into other subjects. A course in Physics teaches us problem solving techniques and ways of thinking that can be applied in other areas. Physics teaches us how to collect and analyse data and then how to explain our measurements in terms of fundamental laws. Physics is highly rated as a "facilitating" subject by the major universities. Many university courses require particular subjects to be studied in the final years of secondary schooling. These are the facilitating subjects. The top 24 universities in the UK, known as the Russell group, publish a document called Informed Choices, giving information for UK university entry. This document states that the top three facilitating subjects in preparation for university study are Mathematics/Further Mathematics, English Literature and Physics.