2VoltageVoltage (V) is the work (W) per charge (Q); it is responsible for establishing current.Work is done as a charge is moved in the electric field from one potential to another.Voltage is the work per charge done against the electric field.
3VoltageDefinitionOne volt is the potential difference (voltage) between two points when one joule of work is used to move one coulomb of charge from one point to the other.
4Voltage Voltage is responsible for establishing current. Sources of voltage include batteries, solar cells, and generators. A Cu-Zn battery, such as you might construct in a chemistry class, is shown.
5CurrentCurrent (I) is the amount of charge (Q) that flows past a point in a unit of time (t).One ampere is a number of electrons having a total charge of 1 C move through a given cross section in 1 s.Question:What is the current if 2 C passes a point in 5 s?0.4 A
6Resistance Resistance is the opposition to current. One ohm (1 W) is the resistance if one ampere (1 A) is in a material when one volt (1 V) is applied.Conductance is the reciprocal of resistance.Components designed to have a specific amount of resistance are called resistors.
8Review of V, I and R Voltage is the amount of energy per charge available tomove electrons from one point to another in a circuit.Current isthe rate of charge flow and is measured inamperes.Resistance isthe opposition to current and is measuredin ohms.
9Fundamental Law Question: The most important fundamental law in electronics is Ohm’s law, which relates voltage, current, and resistance.Georg Simon Ohm ( ) studied the relationship between voltage, current, and resistance and formulated the equation that bears his name.Question:What is the current in from a 12 V source if the resistance is 10 W?1.2 A
10Ohm’s Law Question: If you need to solve for voltage, Ohm’s law is: What is the voltage across a 680 W resistor if the current is 26.5 mA?18 V
11Ohm’s Law Question: If you need to solve for resistance, Ohm’s law is: What is the (hot) resistance of the bulb?Question:115 V132 W
12Resistance/Conductance A student takes data for a resistor and fits the straight line shown to the data. What is the resistance and the conductance of the resistor?Graph of Current versus VoltageThe slope represents the conductance.The reciprocal of the conductance is the resistance:
13Graph of Current vs. Voltage 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 kWWhat is its conductance?0.37 mS
14Graph of Current vs. Resistance If resistance is varied for a constant voltage, the current verses resistance curve plots a hyperbola.Question:What is the curve for a 3 V source?
15Application of Ohm’s Law 26.8 mAThe resistor is green-blue brown-gold. What should the ammeter read?
16TroubleshootingSome questions to ask before starting any troubleshooting are:Has the circuit ever worked?If the circuit once worked, under what conditions did it fail?What are the symptoms of the failure?What are the possible causes of the failure?
17TroubleshootingPlan the troubleshooting by reviewing pertinent information:SchematicsInstruction manualsReview when and how the failure occurred.
18TroubleshootingYou may decide to start at the middle of a circuit and work in toward the failure. This approach is called half-splitting.Based on the plan of attack, look over the circuit carefully and make measurements as needed to localize the problem. Modify the plan if necessary as you proceed.
19Key Terms Linear Ohm’s law Troubleshooting Characterized by a straight-line relationship.A law stating that current is directly proportional to voltage and inversely proportional to current.A systematic process of isolating, identifying, and correcting a fault in a circuit or system.
20Quiz1. Holding the voltage constant, and plotting the current against the resistance as resistance is varied will form aa. straight line with a positive slopeb. straight line with a negative slopec. parabolad. hyperbola
21Quiz2. When the current is plotted against the voltage for a fixed resistor, the plot is aa. straight line with a positive slopeb. straight line with a negative slopec. parabolad. hyperbola
22Quiz3. For constant voltage in a circuit, doubling the resistance meansa. doubling the currentb. halving the currentc. there is no change in the currentd. depends on the amount of voltage
23Quiz4. A four-color resistor has the color-code red-violet-orange-gold. If it is placed across a 12 V source, the expected current isa mAb mAc mAd mA
24Quiz5. If the current in a 330 W resistor is 15 mA, the applied voltage is approximatelya. 5.0 Vb. 22 Vc. 46 Vd. 60 V
25Quiz6. The current in a certain 4-band resistor is 22 mA when the voltage is 18 V. The color bands on the resistor area. blue-gray-red-goldb. red-red-brown goldc. gray-red-brown-goldd. white-brown-red-gold
26Quiz 7. The circuit with the largest current is a. (a) b. (b) c. (c) d. (d)
27Quiz 8. The circuit with the smallest current is a. (a) b. (b) c. (c) d. (d)
28Quiz 9. Before troubleshooting a faulty circuit you should find out a. If the circuit ever workedb. The conditions that existed when it failedc. The symptoms of the failured. All of the above
29Quiz10. A troubleshooting method that starts in the middle and works toward a fault isa. short-circuit testingb. comparison testingc. half-splittingd. resistance testing