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Electricity

Electricity. Electricity. Flow of electric charges (electrons) How much? Current ( I ) I = Δ q/ Δ t (A). V. C. Ohm’s Law. I = V/R R : Resistance ( Ω ) R = ρ L/A ρ : Resistivity ρ Cu = 1.72x10 -8 ρ Al = 2.82x10 -8 ρ Au = 2.44x10 -8 ρ rubber = 10 13 -10 16.

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Electricity

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  1. Electricity

  2. Electricity • Flow of electric charges (electrons) • How much? Current (I) • I = Δq/ Δt (A) V C

  3. Ohm’s Law I = V/R R : Resistance (Ω) R = ρ L/A ρ : Resistivity ρ Cu = 1.72x10-8 ρ Al = 2.82x10-8 ρ Au = 2.44x10-8 ρ rubber = 1013-1016

  4. What is the resistance of a 35m long 20 gauge extension cord? • 20 gauge: A = 5.2 x10-7 m2

  5. What is the resistance of a 75m long 16 gauge extension cord? • 16 gauge: A = 13 x10-7 m2

  6. We can use a resistor to restrict the flow of electricity. Water Pipe Analogy V = pressure I = flow R = size of pipe V R -Change in voltage around entire loop must be zero!

  7. Resistors in series • Several resistors in series behave like one larger resistor: Resistance increases. • RE = R1 + R2 + R3 + ………. 1Ω 2Ω 3Ω

  8. Resistors in Parallel • Several resistors in parallel give more opportunity for the charge to pass: Resistance decreases. • 1/RE = 1/R1 + 1/R2 + 1/R3 + ………. 1Ω 2Ω 3Ω

  9. What is the equivalent Resistance of the entire circuit? R1 = 10Ω R2 = 5Ω R3 = 20Ω R4 = 15Ω 20V

  10. What is V1 the voltage across R1?What is V4 the voltage across R4? R1 = 10Ω R2 = 5Ω R3 = 20Ω R4 = 15Ω 20V

  11. What is V3 the voltage across R3? R1 = 10Ω R2 = 5Ω R3 = 20Ω R4 = 15Ω 20V

  12. Power • P = work/time (J/s) or (Watt) • P = I* V • The “Power” company charges you by the Kilowatt Hour or Kwhr. What unit are they really charging?

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