5. Electricity and magnetism

5. Electricity and magnetism

5.1 – Electric fields

Nature of science:

  • Modelling: Electrical theory demonstrates the scientific thought involved in the development of a microscopic model (behaviour of charge carriers) from macroscopic observation. The historical development and refinement of these scientific ideas when the microscopic properties were unknown and unobservable is testament to the deep thinking shown by the scientists of the time.

Understandings:

  • Charge

  • Electric field

  • Coulomb’s law

  • Electric current

  • Direct current (dc)

  • Potential difference

Applications and skills:

  • Identifying two forms of charge and the direction of the forces between them

  • Solving problems involving electric fields and Coulomb’s law

  • Calculating work done in an electric field in both joules and electronvolts

  • Identifying sign and nature of charge carriers in a metal

  • Identifying drift speed of charge carriers

  • Solving problems using the drift speed equation

  • Solving problems involving current, potential difference and charge

5.2 – Heating effect of electric currents

Nature of science:

  • Peer review: Although Ohm and Barlow published their findings on the nature of electric current around the same time, little credence was given to Ohm. Barlow’s incorrect law was not initially criticized or investigated further. This is a reflection of the nature of academia of the time with physics in Germany being largely non-mathematical and Barlow held in high respect in England. It indicates the need for the publication and peer review of research findings in recognized scientific journals.

Understandings:

  • Circuit diagrams

  • Kirchhoff’s circuit laws

  • Heating effect of current and its consequences

  • Resistance expressed as R=VI

  • Ohm’s law

  • Resistivity

  • Power dissipation

Applications and skills:

  • Drawing and interpreting circuit diagrams

  • Identifying ohmic and non-ohmic conductors through a consideration of the V/I characteristic graph

  • Solving problems involving potential difference, current, charge, Kirchhoff’s circuit laws, power, resistance and resistivity

  • Investigating combinations of resistors in parallel and series circuits

  • Describing ideal and non-ideal ammeters and voltmeters

  • Describing practical uses of potential divider circuits, including the advantages of a potential divider over a series resistor in controlling a simple circuit

  • Investigating one or more of the factors that affect resistance experimentally

5.3 – Electric cells

Nature of science:

  • Long-term risks: Scientists need to balance the research into electric cells that can store energy with greater energy density to provide longer device lifetimes with the long-term risks associated with the disposal of the chemicals involved when batteries are discarded.

Understandings:

  • Cells

  • Internal resistance

  • Secondary cells

  • Terminal potential difference

  • Emf

Applications and skills:

  • Investigating practical electric cells (both primary and secondary)

  • Describing the discharge characteristic of a simple cell (variation of terminal potential difference with time)

  • Identifying the direction of current flow required to recharge a cell

  • Determining internal resistance experimentally

  • Solving problems involving emf, internal resistance and other electrical quantities

5.4 – Magnetic effects of electric currents

Nature of science:

  • Models and visualization: Magnetic field lines provide a powerful visualization of a magnetic field. Historically, the field lines helped scientists and engineers to understand a link that begins with the influence of one moving charge on another and leads onto relativity.

Understandings:

  • Magnetic fields

  • Magnetic force

Applications and skills:

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

  • Determining the direction of force on a current-carrying conductor in a magnetic field

  • Sketching and interpreting magnetic field patterns

  • Determining the direction of the magnetic field based on current direction

  • Solving problems involving magnetic forces, fields, current and charges

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