2 A Basic Circuit All circuits have three (3) main parts: Source of NRGClosed PathDevice which uses the NRG*If not a closed path (open circuit), the device will not work
3 Potential DifferenceWithin a battery, a chemical reaction occurs. Electrons are transferred from one terminal (leaving it positively charged) to another (leaving it negatively charged). A potential difference (voltage) exists between the two terminals.Electromotive Force (EMF) – maximum potential difference a power source can have.Not actually a force but an amount of NRG per chargeV = J/C (Joules/Coulomb)
4 Battery exampleChemical reaction in a battery maintains a difference of 12 volts (12 J/C) of between positive/negative terminalsSymbol for battery
5 Reason for charge movement Battery creates an electric field within (parallel to) wireDirected toward negative terminalIt is this field that exerts a force on the free electrons in the wireTherefore, electrons will moveN.S.L. F = ma
6 Comparison with water flow A pump works due to 2 principlesPressure differenceCertain amount of flow that passes each secondCircuit works due to 2 principlesPotential difference - VoltageCertain amount of charge that flows each second - Current
7 CurrentCurrent is defined as the rate at which charge flows through a surface (imaginary)Current is the same direction as the flow of positive charge.
8 ResistanceResistance (R) – is defined as the restriction of electron flow. It is due to interactions that occur at the atomic scale. For example, as electron move through a conductor they are attracted to the protons on the nucleus of the conductor itself. This attraction doesn’t stop the electrons, just slow them down a bit and cause the system to waste energy.The unit for resistance is the OHM, W
9 Electric PowerPower is the rate at which work is done or energy is dissipatedAs charge moves through a device, the charge loses electric potential energy.L.O.C.O.E. tells us that the decreases in EPE must be accompanied by a transferof energy to some other form (or forms).The charge in a circuit can also gain electrical energy. As it moves through thebattery, the charge goes from a lower potential to a higher potential. The oppositehappens in the electrical device. L.O.C.O.E says this increase in NRG must comefrom somewhere – chemical energy stored in the battery
11 Ways to Wire a CircuitThere are two (basic) ways to wire a circuit. Keep in mind that a resistor can be anything; light bulb, toaster, etc.Series - one after anotherParallel – between a set of junctions andparallel to each other
12 Schematic SymbolsFor the battery symbol, the LONG line is considered to be the POSITIVE terminal and the SHORT line is considered to be the NEGATIVE terminalThe VOLTMETER and AMMETERare special devices you place in oraround the circuit to measureVOLTAGE and CURRENT
13 Series Circuit In a series circuit, the resistors are wired one after another.Since they are all part of theSAME LOOP they eachexperience the SAME amountof CURRENT. Notice in thefigure, they all exist BETWEENthe terminals of the battery – meaningthey SHARE the same POTENTIAL(voltage).
14 Series CircuitAs the current goes through the circuit, the charges must USE ENERGY to get through the resistor. So each individual resistor will get its own individual potential voltage). We call this VOLTAGE DROP.Note: They may use the terms “effective” or “equivalent” to mean TOTAL!
15 Example A series circuit is shown to the left. What is the total resistance?What is the total current?What is the current across EACH resistor? What is the voltage drop across each resistor?( Apply Ohm's law to each resistor separately)Req = = 6WDV=IR =I(6) I = 2AThey EACH get 2 amps!V1W=(2)(1)= 2 V V3W=(2)(3)= 6V V2W=(2)(2)= 4VNotice that the individual VOLTAGE DROPS add up to the TOTAL!!
16 Parallel CircuitIn a parallel circuit, we have multiple loops. So the current splits up among the loops with the individual loop currents adding to the total currentJunctionsIt is important to understand that parallel circuits will all have some position where the current splits and comes back together. We call these JUNCTIONS.The current going IN to a junction will always equal the current going OUT of a junction.
17 Parallel CircuitNotice that the JUNCTIONS both touch the POSTIVE and NEGATIVE terminals of the battery. That means you have the SAME potential difference down EACH individual branch of the parallel circuit. This means that the individual voltages drops are equal.DVThis junction touches the POSITIVE terminalThis junction touches the NEGATIVE terminal
18 ExampleTo the left is an example of a parallel circuit. a) What is the total resistance? b) What is the total current? c) What is the voltage across EACH resistor? d) What is the current drop across each resistor? (Apply Ohm's law to each resistor separately)2.20 W3.64 A8 V each!Notice that the individual currents ADD to the total.1.6 A1.14 A0.90 A
19 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?
20 Compound (Complex) Circuits Suppose the potential difference (voltage) is equal to 120V. What is the total current?1.06 AWhat is the VOLTAGE DROP across the 80W resistor?84.8 V
21 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 AAdd to 1.06A35.2 V Each!0.704 A