# Lec02 - Lecture 2-1 How strong are Coulomb forces...

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Unformatted text preview: Lecture 2-1 How strong are Coulomb forces? •Electron and proton in a hydrogen atom •Compare electric and gravitational forces 2 2 2 p e e g mm e F k F G r r = = electron and proton 2 39 2.2710 e g p e F ke F Gmm = ≈ × 9 2 2 19 7 2 2 1 2 1 2 (8.9910 / )(1.6010 ) (10) (5.310 ) e F k Nm C C O N m r − − − × × ≈ ≈ = × 7 23 2 30 (10) (10) / (10 ) / e a F O N O ms O kg m − − ≈ ≈ = Lecture 2-2 Principle of Superposition ⋯ a a a a + + + = 14 13 12 1 F F F F q 1 q 2 q 3 F 13 F 12 F 1 • Add by components or • Magnitude and direction separately by using trigonometry Lecture 2-3 Electric Field The net Coulomb force on a given charge is always proportional to the strength of that charge. Define electric field , which is independent of the test charge, q, and depends only on position in space: F E q = ca ca 2 1 ˆ 4 F Q E r q r π ε = = a a Electric Field due to a Point Charge Q Lecture 2-4 Electric Field With this concept, we can “map”the electric field anywhere in space produced by any arbitrary: a Vector field 77 82 83 68 55 66 83 75 80 90 91 75 71 80 72 84 73 57 88 92 77 56 88 73 64 Lecture 2-5 Electric Field due to Multiple Point Charges The force on a test charge is then given by ⋯ a a a a + +...
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## This note was uploaded on 04/27/2008 for the course PHYS 241 taught by Professor Wei during the Spring '08 term at Purdue.

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Lec02 - Lecture 2-1 How strong are Coulomb forces...

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