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. Large Hadron Collider is now creating proton collisions at 7 TeV (That’s 7 trillion electron Volts) Most energetic collisions seen in a particle accelerator Less energy than two flies colliding Less energy than most energetic cosmic rays colliding with atoms in upper atmosphere Slide 22-11
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. Slide 22-11
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. 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. Resistivity The resistance of a wire depends on its dimensions and the resistivity of its material: Slide 22-14
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. Would the following changes A.increase the current B.decrease the current C.cause no change 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 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. Clicker Question 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