Physics 212 Lecture 2: Coulombs Law

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Physics 212 Lecture 2 Coulombs Law Electric
Fields

• Charge/Mass Comparison
• Both have FIELD forces surrounding them
• Equations governing behavior of these field
  forces have same form

kg (kilogram)
g (gravitational)
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Electric Field and Force Relationship
Note Can combine the forms of the force
equation to get the electric field E
Note Electric fields and electric forces follow
the superposition theorem
Note qo test charge placed in electric field
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Working with Force Vectors - take care with
directions
F12 force exerted by charge 1 on charge 2 F12
-F21 r unit vector directed from charge 1 to
charge 2 Diagram draw force and unit vectors
for two positive charges (repulsive) Diagram
draw force and unit vectors for one positive
one negative charge (attractive)
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Example Ch 23 6Two 10g Ag spheres 1m apart.
Find fraction of e- moved from one to the other
to get 1x104N force between them. Note that Ag
has 47e- and molar mass is 107.87g/mol
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Example Ch 23 18Three charges at corners of
equilateral triangle as in Fig P23.7. a) Find
E at 2uC charge due to othersb) Find force on
2uC charge