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Current Conservation of current Batteries Resistance and resistivity Simple circuits

Chapter 22 Current and Resistance. Current Conservation of current Batteries Resistance and resistivity Simple circuits. 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.

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Current Conservation of current Batteries Resistance and resistivity Simple circuits

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  1. Chapter 22 Current and Resistance • Current • Conservation of current • Batteries • Resistance and resistivity • Simple circuits 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

  2. Reading Quiz The charge carriers in metals are A. electrons B. positrons C. protons D. a mix of protons and electrons Slide 22-2

  3. Answer The charge carriers in metals are A. electrons Slide 22-3

  4. Reading Quiz 2. A battery is connected to a resistor. Increasing the resistance of the resistor will A. increase the current in the circuit. B. decrease the current in the circuit. C. not affect the current in the circuit. Slide 22-4

  5. Answer 2. A battery is connected to a resistor. Increasing the resistance of the resistor will B. decrease the current in the circuit. Slide 22-5

  6. Reading Quiz 3. A battery is connected to a resistor. As charge flows, the chemical energy of the battery is dissipated as A. current B. voltage C. charge D. thermal energy Slide 22-6

  7. Answer 3. A battery is connected to a resistor. As charge flows, the chemical energy of the battery is dissipated as D. thermal energy Slide 22-7

  8. Batteries The potential difference between the terminals of a battery, often called the terminal voltage, is the battery’s emf. Wchem q ____ ∆Vbat = = Slide 22-12

  9. Definition of a Current Slide 22-9

  10. Student Current Demo What happens as conductor gets longer What happens as conductor gets wider What happens as conductor gets hotter Potential, Charge, and Field Circuit Model Charge and Current (need to load before class) Slide 22-3

  11. Conservation of Current Slide 22-10

  12. Rank the bulbs in the following circuit according to their brightness, from brightest to dimmest. Slide 22-11

  13. Simple Circuits The current is determined by the potential difference and the resistance of the wire: ∆Vchem R _____ I = Slide 22-13

  14. Resistivity The resistance of a wire depends on its dimensions and theresistivityof its material: Slide 22-14

  15. 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? • Which would decrease the current? • Which would cause no change? • Increasing the length of the wire • Keeping the wire the same length, but making it thicker • Using a battery with a higher rated voltage • Making the wire into a coil, but keeping its dimensions the same • Increasing the temperature of the wire Slide 22-15

  16. Power in Circuits Slide 22-19

  17. Checking Understanding • 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 • 1.0 W • 2.0 W • 3.0 W • 4.0 W Slide 22-20

  18. Answer • 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 22-21

  19. Electric Blankets • 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? • 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? Slide 22-22

  20. Additional Clicker Questions A set of lightbulbs have different rated voltage and power, as in the table below. Which one has the highest resistance? Bulb Rated voltage Rated power A 10 V 1 W B 8 V 1 W C 12 V 2 W D 6 V 2 W E 3 V 3 W Slide 22-23

  21. Answer A set of lightbulbs have different rated voltage and power, as in the table below. Which one has the highest resistance? Bulb Rated voltage Rated power A 10 V 1 W Slide 22-24

  22. Kirchhoff’s Laws Slide 23-11

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