Phys.219-Lec02-2011

Phys.219-Lec02-2011 - Lecture 2-1 Coulombs Law Charges with...

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Lecture 2-1 Coulomb’s Law Charges with the same sign repel each other, and charges with opposite signs attract each other. The electrostatic force between two particles is proportional to the amount of electric charge that each possesses and is inversely proportional to the distance between the two squared. 12 2 qq Fk r = Coulomb constant: by 1 on 2 & by 2 on 1 2 2 9 0 / 10 99 . 8 4 1 C m N k × = = πε where ε 0 is called the permittivity constant. ( ) 12 2 2 0 8.85 10 / C Nm ε  = ×⋅ 
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Lecture 2-2 Example: Q = +10 μC q = -1 μC What is the magnitude of force on Q ? On q ? What is the direction of force on Q ? On q ?
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Lecture 2-3 How strong are Coulomb forces? • Electron and proton in a hydrogen atom • Compare electric and gravitational forces 2 22 pe eg mm e Fk F G rr = = electron and proton 2 39 2.27 10 e g F ke F Gm m = ≈× 9 2 2 19 7 2 2 1 2 12 (8.99 10 / )(1.60 10 ) (10 ) (5.3 10 ) e Nm C C ON m r ×× ≈≈ = × 7 23 2 30 / (10 ) / e aF O ms O kg m =
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Lecture 2-4 Principle of Superposition 21 31 net F FF = ++  Add by components or Magnitude and direction separately by using trigonometry
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Lecture 2-5 Example 1: Example 2: Q 2Q
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Phys.219-Lec02-2011 - Lecture 2-1 Coulombs Law Charges with...

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