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Essential idea: Electric charges and masses each influence the space around them and that influence can be represented through the concept of 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)
Understandings:
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
Guidance:
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:
Theory of knowledge:
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
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