Describing fields

Nature of science:

Paradigm shift: The move from direct, observable actions being responsible for influence on an object to acceptance of a field’s “action at a distance” required a paradigm shift in the world of science. (2.3)

• Gravitational fields
• Electrostatic fields
• Electric potential and gravitational potential
• Field lines
• Equipotential surfaces

Applications and skills:

• Representing sources of mass and charge, lines of electric and gravitational force, and field patterns using an appropriate symbolism
• Mapping fields using potential
• Describing the connection between equipotential surfaces and field lines

• Although gravitational and electrostatic forces decrease with the square of distance and will only become zero at infinite separation, from a practical standpoint they become negligible at much smaller distances. How do scientists decide when an effect is so small that it can be ignored?

Utilization:

• Knowledge of vector analysis is useful for this sub-topic (see Physics sub-topic 1.3)

Aims:

• Aim 9: models developed for electric and gravitational fields using lines of forces allow predictions to be made but have limitations in terms of the finite width of a line

• Electrostatic fields are restricted to the radial fields around point or spherical charges, the field between two point charges and the uniform fields between charged parallel plates
• Gravitational fields are restricted to the radial fields around point or spherical masses and the (assumed) uniform field close to the surface of massive celestial bodies and planetary bodies
• Students should recognize that no work is done in moving charge or mass on an equipotential surface

Data booklet reference: