Lecture02_Kim

Lecture02_Kim - 1 Lecture 2-1 Coulomb’s Law(Review q 1 q...

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Unformatted text preview: 1/13/2012 1 Lecture 2-1 Coulomb’s Law (Review) q 1 q 2 r 1,2 r → ɵ 2 2 9 / 10 99 . 8 4 1 C m N k ⋅ × = = πε where ε is called the permittivity constant. • Coulomb constant: 1 2 2 ˆ q q F k r r = a 1,2 1,2 1,2 by 1 on 2 Lecture 2-2 Electric Force (or Coulomb Force) • The electric force is given by • The electric force, unlike the gravitational force, can be positive or negative – If the charges have opposite signs, the force is negative • Attractive – If the charges have the same sign, the force is positive • Repulsive F = k q 1 q 2 r 2 +- +-- + 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 πε = = a a Electric Field due to a Point Charge Q N V C m = (V stands for volts) E points away from positive charges and toward negative charges. Lecture 2-4 Electric Field With this concept, we can “map” the electric field anywhere in space produced by any arbitrary set of charges: 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 1/13/2012 2 Lecture 2-5 Electric Field due to Multiple Point Charges The force on a test charge q by the another charge q i is given by ⋯ a a a a + + + = 3 2 1 F F F F so the electric field is, by definition, given by ⋯ a a a ⋯ a a a a a + + + = + + + = = 3 2 1 3 2 1 E E E q F q F q F q F E Principle of Superposition!...
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Lecture02_Kim - 1 Lecture 2-1 Coulomb’s Law(Review q 1 q...

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