How many laws are named after Kirchhoff?

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circuit elements. Chapter Goal: To understand the fundamental physical principles that govern electric circuits.

1 Chapter 32. Fundamentals of Circuits Surprising as it may seem, the power of a computer is achieved simply by the controlled flow of charges through tiny wires and circuit elements. Chapter Goal: To understand the fundamental physical principles that govern electric circuits. Chapter 32. Fundamentals of Circuits Topics: Circuit Elements and Diagrams Kirchhoff s Laws and the Basic Circuit Energy and Power Series Resistors Real Batteries Parallel Resistors Resistor Circuits Getting Grounded 1 RC Circuits 2 How many laws are named after Kirchhoff? Chapter 32. Reading Quizzes A. 0 B. 1 C. 2 D. 3 E

2 How many laws are named after Kirchhoff? A. 0 B. 1 C. 2 D. 3 E. 4 What property of a real battery makes its potential difference slightly different than that of an ideal battery? A. Short circuit B. Chemical potential C. Internal resistance D. Effective capacitance E. Inductive constant 5 6 What property of a real battery makes its potential difference slightly different than that of an ideal battery? In an RC circuit, what is the name of the quantity represented by the symbol τ? A. Short circuit B. Chemical potential C. Internal resistance D. Effective capacitance E. Inductive constant A. Period B. Torque C. Terminal voltage D. Time constant E. Coefficient of thermal expansion 7 8

3 In an RC circuit, what is the name of the quantity represented by the symbol τ? A. Period B. Torque C. Terminal voltage D. Time constant E. Coefficient of thermal expansion Which of the following are ohmic materials: A. batteries. B. wires. C. resistors. D. Materials a and b. E. Materials b and c Which of the following are ohmic materials: The equivalent resistance for a group of parallel resistors is A. batteries. B. wires. C. resistors. D. Materials a and b. E. Materials b and c. A. less than any resistor in the group. B. equal to the smallest resistance in the group. C. equal to the average resistance of the group. D. equal to the largest resistance in the group. E. larger than any resistor in the group

The equivalent resistance for a group of parallel resistors is A. less than any resistor in the group. B. equal to the smallest resistance in the group. C.

4 The equivalent resistance for a group of parallel resistors is A. less than any resistor in the group. B. equal to the smallest resistance in the group. C. equal to the average resistance of the group. D. equal to the largest resistance in the group. E. larger than any resistor in the group. Chapter 32. Basic Content and Examples

5 Tactics: Using Kirchhoff s loop law Tactics: Using Kirchhoff s loop law 19 20

6 Energy and Power The power supplied by a battery is QUESTION: EXAMPLE 32.4 The power of light The units of power are J/s, or W. The power dissipated by a resistor is Or, in terms of the potential drop across the resistor EXAMPLE 32.4 The power of light EXAMPLE 32.4 The power of light 23 24

7 EXAMPLE 32.4 The power of light Series Resistors Resistors that are aligned end to end, with no junctions between them, are called series resistors or, sometimes, resistors in series. The current I is the same through all resistors placed in series. If we have N resistors in series, their equivalent resistance is The behavior of the circuit will be unchanged if the N series resistors are replaced by the single resistor R eq EXAMPLE 32.7 Lighting up a flashlight QUESTION: 27 28

8 EXAMPLE 32.7 Lighting up a flashlight EXAMPLE 32.7 Lighting up a flashlight EXAMPLE 32.7 Lighting up a flashlight EXAMPLE 32.7 Lighting up a flashlight 31 32

9 Parallel Resistors Resistors connected at both ends are called parallel resistors or, sometimes, resistors in parallel. The left ends of all the resistors connected in parallel are held at the same potential V 1, and the right ends are all held at the same potential V 2. The potential differences V are the same across all resistors placed in parallel. If we have N resistors in parallel, their equivalent resistance is EXAMPLE A combination of resistors QUESTION: The behavior of the circuit will be unchanged if the N parallel resistors are replaced by the single resistor R eq EXAMPLE A combination of resistors EXAMPLE A combination of resistors 35 36

10 EXAMPLE A combination of resistors Example: Kirchoff s Rules V + 2 R 1 R 3 R 2 I 3 I 2 I + V 1 I I = I2 + I3 I R + I R = V1 V2 I2R2 IR1 = RC Circuits Consider a charged capacitor, an open switch, and a resistor all hooked in series. This is an RC Circuit. The capacitor has charge Q 0 and potential difference V C = Q 0 /C. There is no current, so the potential difference across the resistor is zero. At t = 0 the switch closes and the capacitor begins to discharge through the resistor. The capacitor charge as a function of time is where the time constant τ is 39 40

11 EXAMPLE Exponential decay in an RC circuit QUESTION: EXAMPLE Exponential decay in an RC circuit EXAMPLE Exponential decay in an RC circuit EXAMPLE Exponential decay in an RC circuit 43 44

12 General Strategy Chapter 32. Summary Slides General Strategy General Strategy 47 48

13 Important Concepts Important Concepts Important Concepts Applications 51 52

14 Applications Chapter 32. Questions Which of these diagrams represent the same circuit? Which of these diagrams represent the same circuit? A. a and b B. b and c C. a and c D. a, b, and d E. a, b, and c A. a and b B. b and c C. a and c D. a, b, and d E. a, b, and c 55 56

15 What is V across the unspecified circuit element? Does the potential increase or decrease when traveling through this element in the direction assigned to I? What is V across the unspecified circuit element? Does the potential increase or decrease when traveling through this element in the direction assigned to I? A. V decreases by 2 V in the direction of I. B. V increases by 2 V in the direction of I. C. V decreases by 10 V in the direction of I. D. V increases by 10 V in the direction of I. E. V increases by 26 V in the direction of I. A. V decreases by 2 V in the direction of I. B. V increases by 2 V in the direction of I. C. V decreases by 10 V in the direction of I. D. V increases by 10 V in the direction of I. E. V increases by 26 V in the direction of I Rank in order, from largest to smallest, the powers P a to P d dissipated in resistors a to d. Rank in order, from largest to smallest, the powers P a to P d dissipated in resistors a to d. A. P b > P a = P c = P d B. P b = P d > P a > P c C. P b = P c > P a > P c D. P b > P d > P a > P c E. P b > P c > P a > P d A. P b > P a = P c = P d B. P b = P d > P a > P c C. P b = P c > P a > P c D. P b > P d > P a > P c E. P b > P c > P a > P d 59 60

16 What is the potential at points a to e? What is the potential at points a to e? A. A. B. B. C. D. E. C. D. E Rank in order, from brightest to dimmest, the identical bulbs A to D. Rank in order, from brightest to dimmest, the identical bulbs A to D. A. C = D > B > A B. A > C = D > B C. A = B = C = D D. A > B > C = D E. A > C > B > D A. C = D > B > A B. A > C = D > B C. A = B = C = D D. A > B > C = D E. A > C > B > D 63 64

17 The time constant for the discharge of this capacitor is The time constant for the discharge of this capacitor is A. 5 s. B. 1 s. C. 2 s. D. 4 s. E. The capacitor doesn t discharge because the resistors cancel each other. A. 5 s. B. 1 s. C. 2 s. D. 4 s. E. The capacitor doesn t discharge because the resistors cancel each other

= (0.400 A) (4.80 V) = 1.92 W = (0.400 A) (7.20 V) = 2.88 W

= (0.400 A) (4.80 V) = 1.92 W = (0.400 A) (7.20 V) = 2.88 W Physics 2220 Module 06 Homework 0. What are the magnitude and direction of the current in the 8 Ω resister in the figure? Assume the current is moving clockwise. Then use Kirchhoff's second rule: 3.00