Electrostatics
Coulomb's law, electric fields, potential
Electrostatics
Coulomb's law: F = kQ1Q2/r squared, where k = 9 x 10 to the 9 N.m squared/C squared. An electric field is the region around a charge where other charges experience a force. Electric field strength: E = F/q = kQ/r squared.
Example
Worked Example
Two charges, Q1 = +3 microC and Q2 = -2 microC, are 0.1 m apart. F = (9 x 10 to 9)(3 x 10 to -6)(2 x 10 to -6)/(0.1) squared = 5.4 N (attractive, opposite charges).
Note
Exam Tip
Like charges repel, unlike charges attract. Field lines point away from positive charges and towards negative charges. Convert microcoulombs to coulombs: 1 microC = 1 x 10 to the -6 C.
Key Vocabulary
Coulomb's lawForce between charges is proportional to their product and inversely proportional to distance squared
Electric fieldThe region around a charge where other charges experience a force
Point chargeA charge concentrated at a single point with no physical size
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Coulomb's law
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