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Chapter 2-3 Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd 1 T. Elsarnagawy, mde207, 311 2 Chapter 2-3 Electrical symbols Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd T. Elsarnagawy, mde207, 311 Chapter 2-3 3 Basic circuit measurements Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd T. Elsarnagawy, mde207, 311 4 Chapter 2-3 Meter symbols Digital Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd Bar graph Analog T. Elsarnagawy, mde207, 311 5 Chapter 2-3 Current measurement Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd T. Elsarnagawy, mde207, 311 Chapter 2-3 Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd 6 T. Elsarnagawy, mde207, 311 7 Chapter 2-3 Current measurement Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd T. Elsarnagawy, mde207, 311 8 Chapter 2-3 Current measurement Ammeter connection (series) + - !!Polarity a shown Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd T. Elsarnagawy, mde207, 311 9 Chapter 2-3 Voltage measurement Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd T. Elsarnagawy, mde207, 311 Chapter 2-3 Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd 10 T. Elsarnagawy, mde207, 311 11 Chapter 2-3 Voltage measurement Voltmeter across the component (parallel) +ve to +ve -ve to -ve Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd T. Elsarnagawy, mde207, 311 Chapter 2-3 12 Resistance measurement Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd T. Elsarnagawy, mde207, 311 Chapter 2-3 Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd 13 T. Elsarnagawy, mde207, 311 Chapter 2-3 14 Resistance measurement Disconnect R then make the measurement Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd T. Elsarnagawy, mde207, 311 15 Chapter 2-3 Safety note Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd T. Elsarnagawy, mde207, 311 16 Chapter 2-3 Physical effects of electrical current Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd T. Elsarnagawy, mde207, 311 17 Chapter 2-3 Ohm’s Law V-I-R Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd T. Elsarnagawy, mde207, 311 18 Chapter 2-3 Review of V, I, and R Voltage is the amount of energy per charge available to move electrons from one point to another in a circuit. Current is the rate of charge flow and is measured in amperes. Resistance is the opposition to current and is measured in ohms. T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd 19 Chapter 2-3 The most important fundamental law in electronics is Ohm’s law, which relates voltage, current, and resistance. Georg Simon Ohm (1787-1854) studied the relationship between voltage, current, and resistance and formulated the equation that bears his name. In terms of current, Ohm’s law states V I R What is the current from a 12 V source if the resistance is 10 W? 1.2 A T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd 20 Chapter 2-3 Ohm’s law If you need to solve for voltage, Ohm’s law is: V IR What is the voltage across a 680 W resistor if the current is 26.5 mA? 18 V T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd 21 Chapter 2-3 Ohm’s law V If you need to solve for resistance, Ohm’s law is: R I What is the (hot) resistance of the bulb? 138 W OFF V Hz V 120 V mV A Range Autorange Touc h/Hold 1s 1s 10 A V 40 mA COM Fused T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd 22 Chapter 2-3 A student takes data for a resistor and fits the straight ofthe Current versus Voltage lineGraph shown to data. What is the resistance and the conductance of the resistor? 16 The slope represents the conductance. 14.8 mA - 0 mA 1.48 mS 10.0 V - 0 V The reciprocal of the conductance is the resistance: R I (mA) G 14 12 8 4 1 1 676 Ω G 1.48 mS 0 V R I 0 2 4 6 8 10 V (V) T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd 23 Chapter 2-3 Graph of Current versus Voltage 10 8.0 Current (mA) Notice that the plot of current versus voltage for a fixed resistor is a line with a positive slope. What is the resistance indicated by the graph? 2.7 kW 6.0 4.0 2.0 What is its conductance? 0.37 mS 0 0 10 20 30 Voltage (V) T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd 24 Chapter 2-3 Graph of Current versus Resistance V IR ? 10 8.0 Current (mA) If resistance is varied for a constant voltage, the current - resistance curve plots a hyperbola. 6.0 4.0 2.0 0 0 What is the curve for a 3 V source? 1.0 2.0 3.0 Resistance (kW ) T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd 25 Chapter 2-3 Application of Ohm’s law 26.8 mA + m DC Am eter - Power Supply V A +15 V Gnd 5 V 2A - + - + T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd Chapter 2-3 26 Selected Key Terms Linear Characterized by a straight-line relationship. Ohm’s law A law stating that current is directly proportional to voltage and inversely proportional to current. Troubleshooting A systematic process of isolating, identifying, and correcting a fault in a circuit or system. T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd 27 Chapter 2-3 1. Holding the voltage constant, and plotting the current against the resistance as resistance is varied will form a a. straight line with a positive slope b. straight line with a negative slope c. parabola d. hyperbola T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd 28 Chapter 2-3 2. When the current is plotted against the voltage for a fixed resistor, the plot is a a. straight line with a positive slope b. straight line with a negative slope c. parabola d. hyperbola T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd Chapter 2-3 29 Quiz 3. For constant voltage in a circuit, doubling the resistance means a. doubling the current b. halving the current c. there is no change in the current d. depends on the amount of voltage T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd Chapter 2-3 30 Quiz 5. If the current in a 330 W resistor is 15 mA, the applied voltage is approximately a. 5.0 V b. 22 V c. 46 V d. 60 V T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd 31 Chapter 2-3 Quiz 7. The circuit with the largest current is a. (a) b. (b) c. (c) d. (d) +12 V R 10 kW +15 V (a) R 15 kW (b) +18 V R 22 kW (c) +24 V R 27 kW (d) T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd 32 Chapter 2-3 Quiz 8. The circuit with the smallest current is a. (a) b. (b) c. (c) d. (d) +12 V R 10 kW +15 V (a) R 15 kW (b) +18 V R 22 kW (c) +24 V R 27 kW (d) T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd Chapter 2-3 33 Quiz Answers: 1. d 6. c 2. a 7. a 3. b 8. c 4. b 9. d 5. a 10. c T.Elsarnagawy, mde207, 311 Principles of Electric Circuits, Conventional Flow, 9th ed. Floyd