Peoples Physics Book Version-2

14.8. Electric Circuits Problem Set http://www.ck12.org

37. The voltage source in the circuit below provides 10 V. The resistor is 200Ωand the capacitor has a value of
    50 μF. What is the voltage across the capacitor after the circuit has been hooked up for a long time?


38. A simple circuit consisting of a 39μF and a 10kΩresistor. A switch is flipped connecting the circuit to a 12 V
    battery.
    a. How long until the capacitor has 2/3 of the total charge across it?
    b. How long until the capacitor has 99% of the total charge across it?
    c. What is the total charge possible on the capacitor?
    d. Will it ever reach the full charge in part c.?
    e. Derive the formula for V(t) across the capacitor.
    f. Draw the graph of V vs. t for the capacitor.
    g. Draw the graph of V vs. t for the resistor.


39. If you have a 39μF capacitor and want a time constant of 5 seconds, what resistor value is needed?

Answers to Selected Problems

1. a. 4.5C b. 2. 8 × 1019 electrons


2. a. 0.11 A b. 1.0 W c. 2. 5 × 1021 electrons d. 3636 W


3. a. 192Ωb. 0.42 W


4. a. 5.4 mV b. 1. 4 × 10 −^8 A c. 7. 3 × 10 −^11 W, not a lot d. 2. 6 × 10 −^7 J


5. left = brighter, right = longer


6. a. 224 V b. 448 W c. 400 W by 100Ωand 48 W by 12Ω


7. b. 8.3 W


8. 0.5A
   9..


9. 0.8A and the 50Ωon the left


10. a. 0.94 A b. 112 W c. 0.35 A d. 0.94 A e. 50, 45 , 75 Ωf. both 50Ωresistors are brightest, then 45Ω, then
    75 Ω


11. a. 0.76 A b. 7.0 W


12. b. 1000 W
    14..


13. a. 9. 1 Ωb 29. 1 Ωc. 10. 8 Ωd.26. 8 Ωe. 1.8A f. 21.5V g. 19.4V h. 6.1V i. 0.24A j. 16 kW


14. a. 3. 66 Ωb. 0.36A c. 1.32 V
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