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5/23/2012 Terms DC Circuits Ch 26 AP Physics C Electric Circuit: A set of electrical components connected so that they provide one or more complete paths for charge movement. Emf: the energy per unit charge supplied by a source of electric current Circuit Analogy That source is a charge pump that force electrons to move in a certain direction Any device that increse the UE of charges circulating in a circuit is a source of emf Symbols These symbols are the common circuit symbols widely used by the community. 1 5/23/2012 Series Circuit - Resistors Series Circuit - Important When 2 or more resistors are connected end to end, they are said to be connected in series Series Circuit There is only one path for the current (flow of charge, think water flow) therefore the current is the same through each resistor Because the + terminal of the power source is at a nonzero electric potential and the – terminal of the power source is at zero electric potential, the voltages must be used up by the end of the circuit. The voltage drop across each resistor adds up to the total voltage available. Series Circuit - Example Vtotal V1 I1 I 2 I 3 I total V2 Vtotal V1 V2 V3 Remember t hat V IR so... I total Rtotal I1 R1 I 2 R2 I 3 R3 Rtotal I cancels and you have : Rtotal R1 R2 R3 R2 R1 R3 V3 I total I1 I2 I3 2 5/23/2012 Parallel Circuit Resistors Parallel Circuit Vtotal V1 V2 V3 I total I1 I 2 I 3 1 When two or more resistors have separate paths for the current to get to the same point Parallel Circuit Example Vtotal Rtotal 1 1 1 R1 R2 R3 Combination Circuit V1 V2 Rtotal R1 R2 R3 V3 I total I1 I2 I3 A circuit that has both series and parallel components 3 5/23/2012 How to Analyze Combos 1. 2. 3. 4. 5. 6. Add Series sections Add Parallel sections Add Series sections Add Parallel sections Keep going Stop at 1 equivalent resistor Kirchhoff’s Rules Junction Rule (conservation of charge) The current into a junction must equal the current out of the junction. Loop Rule (conservation of energy) The sum of all the voltages (drops and gains) around any closed path must be zero. Kirchhoff’s Rules – Equation Form I 0 (junction rule, valid at any junction) V 0 (loop rule, valid for any closed loop) 4 5/23/2012 Using an Ammeter Using a voltmeter Using an ohmmeter RC Circuit - Charging 5 5/23/2012 RC Circuit - Charging RC Circuit - Charging RC Circuit - Discharging RC Circuit - Discharging 6 5/23/2012 RC Circuit - Discharging RC Circuit – Time Constant In the previous equations for charging and discharging the capacitor two important points should be made 1. q = vC 2. τ = RC (this is the time constant for an RC circuit) 7