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CIRCUIT ANALYSIS OHM’S LAW ENGR. VIKRAM KUMAR B.E (ELECTRONICS) M.E (ELECTRONICS SYSTEM ENGG:) MUET JAMSHORO 1 AMPS volts Ammeters measure current in amperes and are always wired in series in the circuit. Voltmeters measure potential in volts and are always wired in parallel in the circuit. 2 battery - + wiring voltmeter ammeter junction terminal V A AC generator Variable resistance resistance capacitor Variable capacitor 3 ELECTRONS INTO LOAD LOAD (RESISTANCE) [ENERGY OUT] ELECTRONS OUT OF LOAD CONDUCTOR CONDUCTOR ELECTRONS OUT OF SOURCE HIGHER ENERGY ELECTRONS ELECTRON PUMP (SOURCE VOLTAGE) [ENERGY IN] ELECTRONS BACK TO SOURCE LOWER ENERGY ELECTRONS 4 Potential In volts (joules / coul) Drop across a resistance Current In amperes (coul / second) Current passing Through the resistor Resistance In ohms (volts / amp) 5 volts current Electrons have More Energy Battery Electrons get An energy boost current Electrons have Less Energy 6 volts Resistor Electrons have Less Energy Energy is lost In the resistor current Electrons have More Energy 7 4.2 - Ohm’s Law Cause Effect Opposition Every conversion of energy from one form to another can be related to this equation. In electric circuits the effect we are trying to establish is the flow of charge, or current. The potential difference, or voltage between two points is the cause (“pressure”), and resistance is the opposition encountered. Ohm’s Law Simple analogy: Water in a hose Electrons in a copper wire are analogous to water in a hose. Consider the pressure valve as the applied voltage and the size of the hose as the source of resistance. The absence of pressure in the hose, or voltage across the wire will result in a system without motion or reaction. A small diameter hose will limit the rate at which water will flow, just as a small diameter copper wire limits the flow of electrons. 9 Ohm’s Law E I R Where: I = current (amperes, A) E = voltage (volts, V) R = resistance (ohms, ) 4.3 - Plotting Ohm’s Law 11 There are three generally types of electrical circuits: (1) Series circuits in which the current created by the voltage source passes through each circuit component in succession. R2 A2 A1 R3 R1 Arrows show Current path Through each component 12 (2) Parallel circuits in which the current created by the voltage source branches with some passing through one component and while the rest of the current passes through other components. R1 A1 R2 A2 R3 A3 Arrows show Current path Through each component Junction or Branching points R4 A4 13 P A R A L L E L R1 A1 R2 A2 R3 A3 (3) Series Parallel circuits or combination circuits which contain series segments and parallel segments. Arrows show Current path Through each component R4 A4 SERIES 14 All electrical circuit analysis requires the use of two fundamental laws called Kirchhoff’s Laws 15 FIRST LAW All current entering a junction point must equal all current leaving that junction point Current Leaving ( I3 ) Current Leaving ( I2 ) Junction point I1 = I2 + I3 Current Entering ( I1 ) 16 SECOND LAW Around any complete loop, the sum of the voltage rises must equal the sum of voltage drops Resistance 1 (voltage drop 1) Resistance 2 (voltage drop 2) Resistance 3 (voltage drop 3) Current flow Complete loop + Battery (voltage rise) - V(Battery) = V1 + V2 + V3 17 V2 Loop #2 R2 A2 Loop #3 Complete current Paths in a circuit V1 R1 A1 Loop #1 EMF + At Battery Kirchhoff’s Laws Around a loop V rises = V drops A loop is a completed Path for current flow 18 When using Kirchhoff’s laws we apply the principles of conventional current flow. When current leaves the positive (+) terminal of a voltage source and enters the negative (-) terminal a voltage rise occurs across the source. If the current enters the positive and exits the negative a of a voltage source a voltage drop occurs across the source. When tracing a current loop, if the assumed direction of the current and the loop direction are the same, a voltage drop occurs across a resistance. If the assumed direction of the current and the loop direction are opposite, a voltage rise occurs across the the resistance. 19 When using Kirchhoff’s laws we apply the principles of conventional current flow. When current leaves the positive (+) terminal of a voltage source and enters the negative (-) terminal a voltage rise occurs across the source. If the current enters the positive and exits the negative a of a voltage source a voltage drop occurs across the source. V=-6v Current flow + V=+6v Battery ( 6 volts) Current flow - 20 When tracing a current loop, if the assumed direction of the current and the loop direction are the same, a voltage drop occurs across a resistance. If the assumed direction of the current and the loop direction are opposite, a voltage rise occurs across the the resistance. Loop direction Assumed Current flow V=-6v A voltage drop resistor V=+6v A voltage rise Loop direction Assumed Current flow 21 22