Slide 1 Chapter 4:Circuits ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 2 2Introduction• There are only four basic ways to interconnect the various components in an electrical circuit.• You must be able to analyze circuits to determine the expected values of the circuit.• You must be able to apply the principles of basic electronics to account for differences between expected values and measured values in a circuit. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 3 34.1 Basic Requirements for Current• The term current flow refers to sustained current flow.• Momentary or transient currents will be considered later.• There are two basic requirements for current flow in a circuit:– Electromotive force (emf)– A complete path for current ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________Slide 4 4EMFEmf is difference of potential that does not decay as charges are transferredComparisons are made between hydrolytic systems and EMF. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 5 5Voltage Source• Electromotive force (emf) is a potential difference that does not decay as charges are transferred.• Electromotive force may be supplied either by batteries or from a power supply.• Ohm’s Law described current flow in a circuit as I = V/R.• If there is no emf in a circuit, the current will be zero. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 6 6Complete Path for Current• The second requirement for current flow is a closed loop between the two terminals of the emf.• For most purposes, an open circuit is considered to have infinite resistance.• An open in any circuit will result in zero current flow.V112 V R110kΩR210kΩR310kΩDoes this circuit represent a closed loop? ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________Slide 7 7Direction of Current•Electron current flows from negative to positive since electrons are negatively charged particles.• Current also flows from relatively negativepotentials to points that are relatively positive.Discuss a-d. (a) represents 3 voltage sources and ground. (b) represents 5 volts connected across a resistor. The arrow represents the direction of current flow---negative to positive. (c) similar to b except connection is to -5 volts. Note direction of arrow. (d) There is no ground. Negative and positive are now relative to the connection points.4.1 End ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 8 84.2a Series Circuits• As a technician, it is important to understand series circuits.•A series circuit is characterized as having only a single pathfor current flow.• Series components are connected such that only a single path exists for current flow without encountering any branches in the circuit.V112 V R310kΩV1120 V X1100V_100W ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 9 9Series Circuits• If every electron that leaves the negative terminal of the power source has only one path for current, then the circuit is a series circuit.• In a series circuit, since there is only one path for current flow, each component of the circuit has the same current flowing through it as flows through the entire circuit.V112 V R110kΩR210kΩR310kΩV112 V R110kΩR210kΩR310kΩR410kΩAre the above series circuits? ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________Slide 10 10Series Circuits: Intuitive relationships• The following principles apply to series circuits:– All currents are equal.– The total resistance is greater than any one resistance.– Total power is greater than any one component dissipation.– Larger resistances have higher voltage drops.– Total voltage is greater than any one component voltage.V1120 V R110kΩR220kΩR330kΩ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 11 11Mathematical Relationships•In a series circuit, the following relationships exist with regard to current, voltage, and resistance:– Current: IA= I1= I2… = In–Resistance: RT= R1+ R2… + Rn–Voltage: VT= V1+ V2… + Vn• The applied voltage in a closed loop is equal to the sum of the component voltage drops. This important relationship is known as Kirchhoff’s Voltage Law.•IA= applied current•RT= Total Resistance•RN= general expression: can be extended indefinitelyV1120 V R110kΩR220kΩR330kΩ ___________________________________ ___________________________________ ___________________________________ ___________________________________