Auto 241 Auto Electricity & Electronics

1. Auto 241Auto Electricity & Electronics • Chapter 5 • Series Circuits

2. OBJECTIVES After studying Chapter 5, the reader should be able to: • Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “A” (General Electrical/Electronic System Diagnosis). • Identify a series circuit. • State Kirchhoff’s voltage law. • Calculate voltage drops in a series circuit. • Explain series circuit laws.

3. SERIES CIRCUITS • A series circuit is a complete circuit that has more than one electrical load where all of the current has only one path to flow through all of the loads.

4. OHM’S LAW AND SERIES CIRCUITS • Ohm’s law can be used to calculate the value of one unknown (voltage, resistance, or amperes) if the other two values are known. • A series circuit with three bulbs. All current flows through all resistances (bulbs). • The total resistance of the circuit is the sum of the total resistance of the bulbs, and the bulbs will light dimly because of the increased resistance and the reduction of current flow (amperes) through the circuit.

5. OHM’S LAW AND SERIES CIRCUITS FIGURE 5-2 A series circuit with two bulbs.

6. KIRCHHOFF’S VOLTAGE LAW • Kirchhoff’s voltage law, concerns voltage drops. It states: • The voltage around any closed circuit is equal to the sum (total) of the voltage drops across the resistances.

7. KIRCHHOFF’S VOLTAGE LAWApplying Kirchhoff’s Voltage Law As current flows through a circuit, the voltage drops in proportion to the amount of resistance in the circuit. Most, if not all, of the resistance should occur across the load such as the bulb in this circuit. All of the other components and wiring should produce little, if any, voltage drop. If a wire or connection did cause a voltage drop, less voltage would be available to light the bulb and the bulb would be dimmer than normal.

8. KIRCHHOFF’S VOLTAGE LAWApplying Kirchhoff’s Voltage Law In a series circuit, the voltage is dropped or lowered by each resistance in the circuit. The higher the resistance, the greater the drop in voltage.

9. KIRCHHOFF’S VOLTAGE LAWApplying Kirchhoff’s Voltage Law • A voltmeter reads the differences of voltage between the test leads. • The voltage read across a resistance is the voltage drop that occurs when current flows through a resistance. A voltage drop is also called an “IR” drop because it is calculated by multiplying the current (l) through the resistance (electrical load) by the value of the resistance (R).

10. KIRCHHOFF’S VOLTAGE LAWUse of Voltage Drops • Voltage drops, due to built-in resistance, are used in automotive electrical systems to drop the voltage in the following examples. • Dash lights • Blower motor

11. KIRCHHOFF’S VOLTAGE LAWVoltage Drops as a Testing Method • Any resistance in a circuit causes the voltage to drop in proportion to the amount of the resistance. • The formula for voltage drop is: • E = I xR where E is the voltage drop and I is the current in the circuit. • Notice that as the value of the resistance (R ) increases, the voltage drop increases.

12. SERIES CIRCUIT LAWS • Electrical loads or resistance connected in series behave following series circuit laws. • Law 1 The total resistance in a series circuit is the sum total of the individual resistances. • Law 2 The current is constant throughout the entire circuit. • Law 3 Although the current (in amperes) is constant, the voltage drops across each resistance in the circuit.

13. SERIES CIRCUIT LAWS In this series circuit with a 2 ohm resistor and a 4 ohm resistor, the current (2 amperes) is the same throughout, even though the voltage drops across each resistor.

14. SERIES CIRCUIT EXAMPLES

15. SERIES CIRCUIT EXAMPLES

16. SERIES CIRCUIT EXAMPLES

17. SERIES CIRCUIT EXAMPLES

18. SUMMARY • In a simple series circuit, the current remains constant throughout, but the voltage drops as current flows through the resistances of the circuit. • The voltage drop across each resistance or load is directly proportional to the value of the resistance compared to the total resistance in the circuit. • The sum (total) of the voltage drops equals the applied voltage (Kirchhoff’s voltage law). • An open or a break anywhere in a series circuit stops all current from flowing.

19. REVIEW QUESTIONS • What is Kirchhoff’s voltage law? • The voltage around any closed circuit is equal to the sum (total) of the voltage drops across the resistances. • What would current (amperes) do if the voltage were doubled in a circuit? • The current flow would double. • What would current (amperes) do if the resistance in the circuit were doubled? • The current would be cut in half. • What is the formula for voltage drop? • In a series circuit, the voltage is dropped or lowered by each resistance in the circuit. The higher the resistance, the greater the drop in voltage

20. CHAPTER QUIZ • The amperage in a series circuit is _____. • The same anywhere in the circuit • Variable in the circuit due to the different resistances • High at the beginning of the circuit and decreases as the current flows through the resistance • Always less returning to the battery than leaving the battery

21. CHAPTER QUIZ 2. The sum of the voltage drops in a series circuit equals the _____. • Amperage • Resistance • Source voltage • Wattage

22. CHAPTER QUIZ 3. If the resistance and the voltage are known, what is the formula for finding the current (amperes)? • E = I xR • I = E xR • R = E xI • I = E/R

23. CHAPTER QUIZ 4. A series circuit has three resistors of 6 ohms each. The voltage drop across each resistor is 4 volts. Technician A says that the source voltage is 12 volts. Technician B says that the total resistance is 18 ohms. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

24. CHAPTER QUIZ 5. If a 12 volt battery is connected to a series circuit with three resistors of 2 ohms, 4 ohms, and 6 ohms, how much current will flow through the circuit? • 1 ampere • 2 amperes • 3 amperes • 4 amperes

25. CHAPTER QUIZ 6. A series circuit has two 10 ohm bulbs. A third 10 ohm bulb is added in series. Technician A says that the three bulbs will be dimmer than when only two bulbs were in the circuit. Technician B says that the current in the circuit will increase. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

26. CHAPTER QUIZ 7. Technician A says that the sum of the voltage drops in a series circuit should equal the source voltage. Technician B says that the current (amperes) varies depending on the value of the resistance in a series circuit. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

27. CHAPTER QUIZ 8. Two light bulbs are wired in series and one bulb burns out (opens). Technician A says that the other bulb will work. Technician B says that the current will increase in the circuit because one electrical load (resistance) is no longer operating. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

28. CHAPTER QUIZ 9. Four resistors are connected to a 12 volt battery in series. The values of the resistors are 10 ohms, 100 ohms, 330 ohms, and 470 ohms. Technician A says that the greatest voltage drop will occur across the 10 ohm resistor. Technician B says that the greatest voltage drop will occur across the 470 ohm resistor. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

29. CHAPTER QUIZ 10. Three light bulbs are wired in series. A fourth bulb is connected to the circuit in series. Technician A says that the total voltage drop will increase. Technician B says that the current (amperes) will decrease. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B