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Announcements

Announcements. Homework for tomorrow… (Ch . 31, CQ8, Probs. 10, 17, & 42) 30.29: Tungsten 30.32: 2.3 x 10 -3 A 30.54: (4.0 μ s )(1 – e - t /2.0 μ s ) Office hours… MW 12:30-1:30 pm TR 9-10 am F 10-11 am Tutorial Learning Center (TLC) hours:

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Announcements

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  1. Announcements • Homework for tomorrow… (Ch. 31, CQ8, Probs. 10, 17, & 42) 30.29: Tungsten 30.32: 2.3 x 10-3 A 30.54: (4.0 μs)(1 – e -t/2.0μs) • Office hours… MW 12:30-1:30 pm TR 9-10 am F 10-11 am • Tutorial Learning Center (TLC) hours: M 8-1 pm, 3-6 pm, W 8-1 pm, 2-6 pm TR 8-6 pm, F 8-2 pm

  2. Chapter 31 Fundamentals of Circuits (Series Resistors & Real Batteries)

  3. Review… Rate at which the battery supplies energy to the charges is..

  4. 31.3:Energy and Power Power dissipated by a resistor..

  5. 31.3:Energy and Power Power dissipated by a resistor.. Notice: For resistors in series, the resistor with the largest resistance dissipates the most power.

  6. Quiz Question 1 Which resistor dissipates more power? • The 9  resistor. • The 1  resistor. • They dissipate the same power.

  7. i.e. 31.4:The Power of Sound Most loudspeakers are designed to have a resistance of 8Ω. If an 8Ω loudspeaker is connected to a stereo amplifier with a rating of 100W, what is the maximum possible current to the loudspeaker?

  8. Kilowatt Hours The energy dissipated by a resistor during time interval Δtis 1 kWh is equivalent to how many J’s?

  9. Quiz Question 2 How does the brightness of bulb B compare to that of bulb A? • Bulb B is brighter. • Bulb A is brighter. • Both bulbs have the same brightness.

  10. 31.4:Series Resistors Consider two resistors in series… • Can we find an equivalent resistor, Req, to the two resistors, R1 & R2? R1 + + Req - - R2

  11. 31.4:Series Resistors Consider two resistors in series… • Can we find an equivalent resistor, Req, to the two resistors, R1 & R2? • YES! R1 + + Req - - R2

  12. 31.4:Series Resistors What about several resistors in series… • Can we find an equivalent resistor, Req, to the resistors, R1, R2,…(all in series)? R1 + + R2 Req - - R3

  13. 31.4:Series Resistors What about several resistors in series… • Can we find an equivalent resistor, Req, to the resistors, R1, R2,…(all in series)? • YES! R1 + + R2 Req - - R3

  14. Series Resistors • A battery provides a fixed emf(potential difference), NOT a fixed current. • The amount of current depends on… • the battery’s emf • the resistance of the circuit attached to the battery.

  15. i.e. 31.5:A series resistor circuit • What is the current in the circuit below? • Draw a graph of potential versus position in the circuit, going cw from V = 0V at the battery’s negative terminal.

  16. Ammeters… • are used to measure currents. • Must be wired in series with the circuit element whose current is to be measured. • Rammeter~0 Ω

  17. 31.5:Real Batteries • have an internal resistance, r • The terminal voltage is… Notice: • only when I = 0, is .

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