Decide if each is true or false:

Decide if each is true or false: • When a battery no longer works it is out of charged particles (electrons) and needs more particles before it can be used again. • A battery is the source of charged particles in a circuit. • Charge is used up as it flows through a circuit. • The electrical utility company supplies millions of electrons to our homes everyday.

All statements were FALSE!! • A dead battery is out of energy required to push charge from one terminal to another • Energy can be restored in some batteries with a reversible chemical reaction…so it is more like reenergizing than recharging your batteries • Batteries are the source of energy in a circuit, charged particles carry the energy • Energy is used in a circuit, not charge • Electrons are already in your home, the power company supplies the energy to move the electrons

Circuits • A set of electrical components connected to a voltage source in one or more complete paths allowing the movement of charges

Circuits: Requirements • All circuits must have three components • A source of energy (potential difference, V) • A closed conducting loop • A device that uses the energy (load) *If ANY part of the circuit is open the device will not work! Load

Types of Circuits • Closed circuit • Path from one terminal to the other is complete. A potential difference exists and electrons move from one terminal to the other. • Open Circuit • No complete path, No charge flow, No current • Short Circuits • No load, so no resistance to charge movement. • Causes high current, damaging circuit components (burns out battery).

High Potential A circuit is like a rollercoaster • It is a complete loop • Energy is put into particles to increase potential energy (a battery in a circuit and the first hill in the rollercoaster) • Moves from high potential energy to low potential energy. Low Potential

Drawing Schematic Circuits What I use • Symbols represent circuit components • Wire • Battery • Resistor • Light bulb • Switch • Open • Closed

EMF (Electromotive Force) • The energy supplied by a source of electric current • From devices that increase the potential energy of electrons moving in a circuit (batteries) • Conventional current flow shows the direction of + charges (+ to -) • EMF shows the actual flow of electrons (- to +) (Source of EMF)

Ways to Wire a Circuit • Series Circuit • A circuit or part of a circuit that provides a single conducting path. • Parallel Circuit • A circuit or part of a circuit in which two or more components are connected at a junction, providing multiple conducting paths for the current

Resistors in Series • Each resistor has the same current since they are all part of the same loop • Itotal = I1 = I2 = I3 • The total (equivalent) resistance is the sum of all resistors • Req= R1 + R2 + R3 • The voltage is shared among resistors • Vtotal = V1 + V2 + V3

Resistors in Parallel • Same potential difference (voltage) across them. • Vtotal = V1 = V2 • The sum of currents equals total current • Itotal = I1 + I2 • Equivalent resistance is the sum of the reciprocals • 1/REQ= 1/R1 + 1/R2

Series vs. Parallel

Example 1: Series • What type of circuit is shown? • What is the total resistance? • What is the total current? • What is the current in each resistor? • What is the voltage across each resistor? Req = 1 + 2 + 3 = 6 W V=IReq 12=I(6) I = 2 A 2 A (same as total) V1Ω = (2)*(1) = 2 V V3Ω = (2)*(3) = 6 V V2Ω = (2)*(2) = 4 V *Notice that the individual voltage drops add up to the total V

Example 2: What type of circuit is shown? What is the total resistance? What is the total current? What is the voltage across each resistor? What is the current in each resistor? Parallel 1/Req = 1/5 + 1/7 + 1/9 Req = 2.2 Ω V = IReq 8 = I*2.2 I = 3.6A 8 V (Same for each, = to battery) 8 = I*5 = 1.6 A 8 = I*7 = 1.1 A 8 = I*9 = 0.90 A *Notice that the individual currents add up to the total I

Practice: Series or Parallel • A 9.0 V battery is connected in series to four resistors with values of 2.0, 4.0, 5.0, and 7.0. Find the equivalent resistance, the total current and the voltage across each resistor in the circuit. • A 9.0 V battery is connected to four resistors in parallel with values of 2.0, 4.0, 5.0, and 7.0. Find the equivalent resistance, the total current and the current through each resistor in the circuit. Req=0.92 Ω Itot=9.8 A Req=18 Ω Itot=0.5 A V2=1V, V4=2V, V5=2.5V, V7=3.5V I2=4.5A, I4=2.3A, I5=1.8A, I7=1.3A

Compound (Complex) Circuits Many times you will have series and parallel in the SAME circuit. Solve this type of circuit from the inside out. WHAT IS THE TOTAL RESISTANCE?

Solving Complex Circuits (steps) Use 12 V source, 1 & 2 ohm series, 6 & 3 ohm parallel • Simplify Circuit • Find Req for parallel part and then redraw circuit as series only • Find Req for new circuit • Find total current using Ohm’s Law • Find voltage drop across each resistor (treat resistors in parallel as 1, use Req) • Find current in resistors in parallel sections using voltage from step #4 & resistors from original drawing

Compound (Complex) Circuits Suppose the potential difference (voltage) is equal to 120V. What is the total current? 1.06 A What is the VOLTAGE DROP across the 80W resistor? 84.8 V

Compound (Complex) Circuits What is the current across the 100W and 50W resistor? What is the VOLTAGE DROP across the 100W and 50W resistor? 0.352 A Add to 1.06A 35.2 V Each! 0.704 A

Hints! • Use a chart to help solve these problems • Remember: • In series, I is same throughout, V changes • In parallel, I changes, V is same throughout

Decide if each is true or false: