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By Louis Hierle - Unknown source, Public Domain, https://commons.wikimedia.org/w/index.php?curid=76393504
THE IB SAYS
THE IB SAYS
Essential idea: When charges move an electric current is created.
Understandings: Charge; Electric field; Coulomb’s law
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
Guidance: Students will be expected to apply Coulomb’s law for a range of permittivity values
Data booklet equations:
My vodcast
My vodcast
Coulomb's law
Coulomb's law
In 1795 Coulomb described a series of investigations of forces and charge. He demonstrated that the force between two charged particles is proportional to the product of their charge and inversely proportional to their separation. Coulomb's Law is another example of an inverse-square law.
As the force calculated is a vector it is possible to combine multiple vectors for multiple charges, but the IB will generally only ask about pairs of forces.
Coulomb's constant and permittivity
Coulomb's constant and permittivity
The constant of proportionality, the Coulomb constant, is defined as k = 9 × 109 Nm2 C-2. However, this is only strictly true in a vacuum. The medium through which an electric field passes has a property called permittivity. For a vacuum this determines the value of k given above, but other media will produce different values.
Additional videos
Additional videos
Good introduction, with example.
A slower burn, does include info on permittivity.
Resources from textbooks
Resources from textbooks
Oxford Physics: pages 172 - 175
Hamper HL (2014): pages 214, includes two exercises
Relevant questions from Dot Point Physics (6 Fields and forces)
Relevant questions from Dot Point Physics (6 Fields and forces)
pages 290 - 292
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