Today in PBS&DResistanceVoltage and CurrentOhm’s lawConnecting ResistancesMeasuring Voltage &CurrentPowerCircuit Analysis:Kirchoff’s LawsAssumptions & DefinitionsDefinitionsKirchoff’s Current Law(KCL)ExampleExampleVoltage DividerKirchoff’s Voltage Law(KVL)More on KVLOpen & Short CircuitsCapacitorsCapacitorsCapacitor CombinationsInductorsInductorsSignals & SinusoidsSinusoidsFrequency , period & PhaseSinusoidsSinusoidsSinusoidsSinusoidsIn MatlabComplex ExponentialSignalsPhasor NotationPhasor Notation in Circuit AnalysisPhasor Notation inCircuit AnalysisImpedanceSeries & Parallel ImpedanceExercisePBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Principles of Biomedical Systems & DevicesPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Principles of Biomedical Systems & DevicesLecture 3:Basic Concepts of ElectronicsPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Today in PBS&D Electronic componentsªResistors, capacitors and inductors Circuit analysisªKirchoff’s lawsªVoltage dividers Common Electrical InstrumentsªAmmeter / VoltmeterªWheatstone bridge The Concept of FrequencyªImpedancePBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404ResistanceA conductor allows an electric current to flow through it, but it does not permit the current to flow with perfect freedom. Collisions between the electrons and the atoms of the conductor interfere with the flow of electrons. This phenomenon is known as resistance. Resistance “resists” the flow of electricity.L2rLALRπρρ==ResistivityThe term resistance is also used when the flow of a fluid or heat is impeded. The forces of friction provide the resistance to the flow of a fluid in a pipe, and insulation provides thermal resistance that reduces the flow of heat from a higher to a lower temperature.?How about the effect of temperature?W=2rThe effect of changing thelength / width of the conductor…??PBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Voltage and CurrentVoltage is the electrical force, or "pressure", that causes current to flow in a circuit. It is measured in VOLTS. Current is the movement of electrical charge - the flow of electrons through the electronic circuit. Current is measured in AMPERES. Similar concepts also appear in other disciplines: For example, in hydraulics:Pictures are from: http://webhome.idirect.com/~jadams/electronics/v_c_r.htmPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Ohm’s lawThe amount of current passing through a conductor is directly proportional to the voltage across the conductor and inversely proportional to the resistance of the conductor. RVI =IRV=V: The voltage difference between twolocations, aka potential difference.It is analogous to pressure.I: The amount of current flowing between these two points. It is analogous to flow.R: Resistance between the two points.+_IVRPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Connecting ResistancesElectric circuits with only a single path for electricity to flow along are called series circuits. Electric circuits with multiple pathways for electricity to flow along are called parallel circuits. A circuit’s total resistance to the flow of electricity is calculated differently for series circuits than it is for parallel circuits.Constant current IConstant voltageHow about connecting power sources ?(that is power supplies, voltages…?)PBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Measuring Voltage &CurrentA device that measures the potential between two points is a voltmeter, whereas a device that measures current along a path is an ammeter. Therefore, a voltmeter is always connected in PARALLELbetween the two points of interest, whereas an ammeter is connected in series along the path of the current. Note that no measurement device is perfect and causes some error on measurement. Hence, both ammeter and voltmeter have internal resistances. If you were the manufacturer, what would you make the internal resistances of these devices…?Serves as the resistance aka, “the load”PBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404PowerA conductor’s resistance to electric current produces heat. The greater the current passing through the conductor, the greater the heat. Also, the greater the resistance, the greater the heat. A current of I amps passing through a resistance of R ohms for t seconds generates an amount of heat equal to Joules (a joule is a unit of energy equal to 0.239 calorie).Energy is required to drive an electric current through a resistance. This energy is supplied by the source of the current, such as a battery or an electric generator. The rate at which energy is supplied to a device is called power, that is power is energy supplied per unit time. Power is often measured in units called Watts. The power P supplied by a current of I amp passing through a resistance of R ohms is given byRtI2dv1∫= ivTEVIRVRIP ===22PBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Circuit Analysis:Kirchoff’s Laws Two sets of rules define circuit analysis:ªKirchoff’s current laws ªKirchoff’s voltage laws KCL: The algebraic sum of all currents in any given node is zero KVL: The algebraic sum of all voltages in any given loop is zeroªWhat is a node?ªWhat is a loop?ªWhat is an algebraic sum…?PBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Assumptions & Definitions Wires: We connect the components to each other by wires. ª Wires, just like any other component in a circuit, has an internal resistance. However, since this resistance is so small, it is usually ignored. We will “model” the wire as a zero-resistance device, just like we model the ideal current meter as a zero-resistance device. Nodes: A node is defined as the point where two or more components are connected to each other. You must show care, however, in locating and counting the nodes.+-vARCRDRFRERBHow many nodes are there in this circuit?PBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Definitions Loops: Any trace that starts and ends at the same point is a “closed loop”. ª A loop typically follows