Series Circuit

Same Current  Two circuit elements joined together end to start are in series. One wire connectionOne wire connection  Electrons don’t pile up in an element as current flows.  The two elements have the same current. May have different voltageMay have different voltage

Series Batteries  Batteries can be joined in series. Joined plus to minus Connecting lines are conductors  Total potential is the sum of individual potentials. Normal battery symbol suggests series V1V1 V2V2 V3V3 V

Series Resistors  Resistors can be joined in series. End doesn’t matter  Ohm’s law gives the voltage drop for each resistor. Sum for total Divide by current  Total resistance is the sum of individual resistances. R1R1 R2R2 R3R3 I

Internal Resistance  Real voltage sources have some internal resistance. Resistor in series with batteryResistor in series with battery  The resistor reduces some voltage from the battery. Same current through internal resistanceSame current through internal resistance Ohm’s law for voltage dropOhm’s law for voltage drop R int I V int V eff

Power  Power in a circuit is measured in watts (W). Joule/secJoule/sec  A watt is a volt times an amp. Voltage times currentVoltage times current  Ohm’s law can be combined with the power formula. Eliminate voltage or currentEliminate voltage or current

Flashlight  A flashlight uses a series circuit. Equivalent batteries and resistancesEquivalent batteries and resistances

Lights On  The flashlight uses two 1.5 V batteries with 10  internal resistance each. The bulb has a resistance of 50 .  Find the current through the flashlight, and the power dissipated by the bulb.  The elements form a series circuit. Total EMF of V = 3.0 V Total resistance of R = 70   Ohm’s law gives the current. I = V/R = 3.0 V / 70  I = A = 43 mA  The power is dissipated through the resistors. P = V 2 / R = 130 mW

Single Loop  A circuit with a complete loop is a closed circuit. All elements in series Interrupted circuit is open  An ammeter measures current and must be in series. Schematic symbol for amps R int I V int V eff R int I V int V eff A

Kirchhoff’s Voltage Law  An electron moving in a circuit loop has some potential increases and some decreases. Increases from batteries, decreases from resistorsIncreases from batteries, decreases from resistors  The work done by the circuit on an electron in a closed loop must be zero. Sum of potential changes must be zeroSum of potential changes must be zero Conservation of energyConservation of energy  This is Kirchhoff’s voltage law. next