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Aim: How can we explain a series circuit? Do Now: Find the resistance of a 0.25 m Tungsten wire with a diameter of 1.5 x 10-3 m. R = ρL A R = (5.6 x 10-8Ω·m) (0.25 m) 1.77 x 10-6 m2 R = 7.9 x 10-3 Ω Circuits • A closed path where current flows (charges flow) • Has a source of potential difference (cell or battery) • Has a resistance (ex: lightbulb) • Has wires Lamp Resistor: hinders flow of charges Wire Provides complete path Switch Dry cell Opens and closes circuit path Source of potential difference – pushes charges, causing them to move Supplies Voltage Opens and closes a circuit Measures Voltage Measures Current Supplies Resistance Light Bulb Demo http://www.youtube.com/watch?v=csTlRvqSITI&feature=r elated If one goes out, they all go out Series Circuits • Has only 1 path for the current to flow • Draw a series circuit with a 9 V battery and 3 resistors reading 100Ω, 300Ω, and 50Ω. Equivalent (Total) Resistance Req = R1 + R2 + R3 Req = 100 Ω + 300 Ω + 50 Ω Req = 450 Ω Draw a new equivalent circuit Req = 450 Ω VT = total voltage of circuit What is the total current? IT = VT RT IT = 9 V 450Ω IT = 0.02 A Current is constant for a series circuit Therefore: I1 = 0.02 A I2 = 0.02 A I3 = 0.02 A When solving vertically, use the rules in the ref. tables for series circuits R(Ω) When solving horizontally, use Ohm’s Law 1 2 3 Total Now solve for V1, V2, and V3 I(A) V(V) V=IR 100 0.02 2 V=IR 300 50 450 0.02 6 V=IR 0.02 0.02 1 9 Check the voltage: VT = V1 + V2 + V3 Draw a 120 V battery in series with 3 resistors. R1 = 2 Ω R2 =4Ω, R3 = 8Ω. 2Ω 4Ω 120 V 8Ω Find Req, then draw equivalent circuit with 1 resistor and an ammeter. Place directly into circuit. 120 V Req = 14 Ω Current is constant in series so it doesn’t matter where the ammeter is placed Note: Voltmeters get placed around what they are measuring Solve for all currents and voltages R(Ω) 1 I(A) V1 = I1R1 2 IT = I1 = I2 = I3 8.57 2 IT = I1 = I2 = I3 4 3 Total V(V) 8 8.57 V1 = (8.57)(2) 17.14 V2 = I2R2 V1 = (8.57)(4) IT = I1 = I2 = I3 34.28 V3 = I3R3 8.57 V1 = (8.57)(8) R1+R2+R3 IT =VT / RT 2+4+8 IT =120/14 68.56 120 V1+V2+V3 14 8.57 17.14+34.28+68.56 Remember to check the voltages!