Electricity Electricity Flow of electric charges electrons V

Electricity

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

Ohm’s Law I = V/R R : Resistance (Ω) R = ρ L/A ρ : Resistivity ρ Cu = 1. 72 x 10 -8 ρ Al = 2. 82 x 10 -8 ρ Au = 2. 44 x 10 -8 ρ rubber = 1013 -1016

What is the resistance of a 35 m long 20 gauge extension cord? • 20 gauge: A = 5. 2 x 10 -7 m 2

What is the resistance of a 75 m long 16 gauge extension cord? • 16 gauge: A = 13 x 10 -7 m 2

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

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

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

What is the equivalent Resistance of the entire circuit? R 1 = 10 Ω 20 V R 2 = 5 Ω R 4 = 15 Ω R 3 = 20 Ω

What is V 1 the voltage across R 1? What is V 4 the voltage across R 4? R 1 = 10 Ω 20 V R 2 = 5 Ω R 4 = 15 Ω R 3 = 20 Ω

What is V 3 the voltage across R 3? R 1 = 10 Ω 20 V R 2 = 5 Ω R 4 = 15 Ω R 3 = 20 Ω

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?