Series Circuit Same Current Two circuit elements joined

Series Circuit

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

Series Batteries V 1 V 2 V 3 ] Batteries can be joined in series. • Joined plus to minus • Connecting lines are conductors ] Total potential is the sum of individual potentials. V • Normal battery symbol suggests series

Series Resistors R 1 I R 2 R 3 ] 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.

Internal Resistance ] Real voltage sources have some internal resistance. • Resistor in series with battery ] The resistor reduces some voltage from the battery. • Same current through internal resistance • Ohm’s law for voltage drop Rint Veff I

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

Flashlight ] A flashlight uses a series circuit. • Equivalent batteries and resistances

Lights On ] The flashlight uses two 1. 5 V batteries with 10 W internal resistance each. The bulb has a resistance of 50 W. ] 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 W ] Ohm’s law gives the current. • I = V/R = 3. 0 V / 70 W • I = 0. 043 A = 43 m. A ] The power is dissipated through the resistors. • P = V 2 / R = 130 m. W

Single Loop Rint Veff Vint I A ] 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

Kirchhoff’s Voltage Law ] An electron moving in a circuit loop has some potential increases and some decreases. • Increases 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 zero • Conservation of energy ] This is Kirchhoff’s voltage law. next