Electricity

Flow of electric charges (electrons) How much? Current ( I ) I = Δq/ Δt (A) VC

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 =

What is the resistance of a 35m long 20 gauge extension cord? 20 gauge: A = 5.2 x10 -7 m 2

What is the resistance of a 75m long 16 gauge extension cord? 16 gauge: A = 13 x10 -7 m 2

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

Resistors in series Several resistors in series behave like one larger resistor: Resistance increases. R E = R 1 + R 2 + R 3 + ………. 1 Ω1 Ω 2 Ω2 Ω 3 Ω3 Ω

Resistors in Parallel Several resistors in parallel give more opportunity for the charge to pass: Resistance decreases. 1/R E = 1/R 1 + 1/R 2 + 1/R 3 + ………. 1 Ω1 Ω 3 Ω3 Ω 2 Ω2 Ω

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

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

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