Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Current Conservation of current Batteries Resistance and resistivity Simple circuits Chapter 22 Current and Resistance Topics: Sample question: How can the measurement of an electric current passed through a person’s body allow a determination of the percentage body fat? Slide 22-1

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Reading Quiz 1.The charge carriers in metals are A. electrons B. positrons C. protons D. a mix of protons and electrons Slide 22-2

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 1.The charge carriers in metals are A. electrons Slide 22-3 Answer

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Light the Bulb Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Can you light a bulb when you have 1 battery 1 Bulb 1 wire A - yes B - no

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Conditions for a circuit Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Properties of a Current Slide 22-8

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Brainstorm: what is used up in a circuit Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Definition of a Current Slide 22-9

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Simple Circuits The current is determined by the potential difference and the resistance of the wire: Slide I = ∆ V chem R _____

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 22-3

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 22-4

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 22-5

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Conservation of Current Slide 22-10

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Demonstration - Conservation of Current Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Rank the bulbs in the following circuit according to their brightness, from brightest to dimmest. A.A  B  C  D B.A  B  C  D C.A  D  B  C D.B  C  A  D Checking Understanding Slide 22-16

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Answer Rank the bulbs in the following circuit according to their brightness, from brightest to dimmest. A.A  B  C  D B.A  B  C  D C.A  D  B  C D.B  C  A  D Slide 22-17

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Resistivity The resistance of a wire depends on its dimensions and the resistivity of its material: Slide 22-22

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Checking Understanding A battery is connected to a wire, and makes a current in the wire. Which of the following changes would increase the current? (1) Increasing the length of the wire; (2) keeping the wire the same length, but making it thicker; (3) using a battery with a higher-rated voltage; (4) making the wire into a coil, but keeping its dimensions the same; (5) increasing the temperature of the wire. A.All of the above B.1 and 5 C.1, 4, and 5 D.2 and 3 E.None of the above Slide 22-23

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Answer A battery is connected to a wire, and makes a current in the wire. Which of the following changes would increase the current? (1) Increasing the length of the wire; (2) keeping the wire the same length, but making it thicker; (3) using a battery with a higher-rated voltage; (4) making the wire into a coil, but keeping its dimensions the same; (5) increasing the temperature of the wire. A.All of the above B.1 and 5 C.1, 4, and 5 D.2 and 3 E.None of the above Slide 22-24

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Kirchhoff’s Laws Slide 23-11

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 1.What happens as conductor gets longer 2.What happens as conductor gets wider 3.What happens as conductor gets hotter Slide 22-3 Student Current Demo Potential, Charge, and Field Circuit Model Charge and Current (need to load before class)

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Simple Circuits The current is determined by the potential difference and the resistance of the wire: Slide I = ∆ V chem R _____

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Checking Understanding A battery is connected to a wire, and makes a current in the wire. i.Which of the following changes would increase the current? ii.Which would decrease the current? iii.Which would cause no change? A.Increasing the length of the wire B.Keeping the wire the same length, but making it thicker C.Using a battery with a higher rated voltage D.Making the wire into a coil, but keeping its dimensions the same E.Increasing the temperature of the wire Slide 22-15

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Power in Circuits Slide 22-19

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. A resistor is connected to a 3.0 V battery; the power dissipated in the resistor is 1.0 W. The battery is now traded for a 6.0 V battery. The power dissipated by the resistor is now A.1.0 W B.2.0 W C.3.0 W D.4.0 W Checking Understanding Slide 22-20

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. A resistor is connected to a 3.0 V battery; the power dissipated in the resistor is 1.0 W. The battery is now traded for a 6.0 V battery. The power dissipated by the resistor is now D.4.0 W Slide Answer

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 1.An electric blanket has a wire that runs through the interior. A current causes energy to be dissipated in the wire, warming the blanket. A new, low-voltage electric blanket is rated to be used at 18 V. It dissipates a power of 82 W. What is the resistance of the wire that runs through the blanket? 2.For the electric blanket of the above example, as the temperature of the wire increases, what happens to the resistance of the wire? How does this affect the current in the wire? The dissipated power? Electric Blankets Slide 22-22

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Additional Clicker Questions 1.A set of lightbulbs have different rated voltage and power, as in the table below. Which one has the highest resistance? BulbRated voltageRated power A10 V1 W B 8 V1 W C12 V2 W D 6 V2 W E 3 V3 W Slide 22-23

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 1.A set of lightbulbs have different rated voltage and power, as in the table below. Which one has the highest resistance? BulbRated voltageRated power A10 V1 W Slide Answer