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Announcements

Announcements. EXAM 2 on Tuesday, March 18! Homework for tomorrow… (Ch . 31, CQ 10, Probs. 20 & 22) CQ3: 3V 30.1: see back of book 30.6: 8V, 22V 30.8: 1.9W, 2.9W 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 • EXAM 2 on Tuesday, March 18! • Homework for tomorrow… (Ch. 31, CQ 10, Probs. 20 & 22) CQ3: 3V 30.1: see back of book 30.6: 8V, 22V 30.8: 1.9W, 2.9W • 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 (Real Batteries & Parallel Resistors)

  3. Review… Power dissipated by a resistor… Resistors in series…. Terminal voltage across a real battery…

  4. Quiz Question 1 The battery current I is • 3 A. • 1.5 A. • 1 A. • 2/3 A. • 1/3 A.

  5. Quiz Question 2 A real battery has an emf, E, and a terminal voltage, ΔVbat, where ΔVbat< E. The voltage drop across the resistor, ΔVR, is equal to • E. • ΔVbat. • both. • neither.

  6. 31.5:Real Batteries Notice: ΔVR = ΔVbat, ΔVR≠ E

  7. i.e. 31.6:Lighting up a flashlight A 6.0Ω flashlight bulb is powered by a 3.0V battery with an internal resistance of 1.0Ω. What are the power dissipation of the bulb and the terminal voltage of the battery?

  8. A Short Circuit… What is the current in this circuit?

  9. A Short Circuit… What is the current in this circuit? Notice: This is the maximum possible current that this battery can produce!

  10. i.e. 31.7:A short-circuited battery What is the short-circuit current of a 12V car battery with an internal resistance of 0.020Ω? What happens to the power supplied by the battery?

  11. Quiz Question 3 Consider the circuit below, where the switch is open. The current is the same through bulbs A and B, and they are equally bright. Bulb C is not glowing. The switch is now closed, what happens to the brightness of A? • It increases. • It decreases. • It stays the same.

  12. 31.6:Parallel Resistors Consider two resistors in parallel… • Can we find an equivalent resistor, Req, to the two resistors, R1 & R2? + + Req R1 R2 - -

  13. 31.6:Parallel Resistors Consider two resistors in parallel… • Can we find an equivalent resistor, Req, to the two resistors, R1 & R2? • YES! + + Req R1 R2 - -

  14. 31.6:Parallel Resistors What about several resistors in parallel… • Can we find an equivalent resistor, Req, to the the resistors, R1, R2,…(all in parallel)? + + R3 Req R1 R2 - -

  15. 31.6:Parallel Resistors What about several resistors in parallel… • Can we find an equivalent resistor, Req, to the the resistors, R1, R2,…(all in parallel)? • YES! + + R3 Req R1 R2 - -

  16. Quiz Question 3 Consider the circuit below, where the switch is open. The current is the same through bulbs A and B, and they are equally bright. Bulb C is not glowing. The switch is now closed, what happens to the brightness of A? • It increases. • It decreases. • It stays the same.

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