ap circuits hw solutions

NAME AP PHYSICS C: E&M

CIRCUITS: HW

1. The circuit shown below has two resistors with R1>R2, Which of the two resistors dissipates the larger amount of power? Explain. (cq4)

2. Initially bulbs A and B (below) are glowing. What happens to each bulb if the switch is closed? Does it get brighter, dimmer, stay the same, or go out? Explain. (cq10)

The resistors are in series so the current through each Is the same: Bulb A would get brighter because the equivalent resistance of the circuit would drop and the current would raise. Bulb B would become dimmer or likely go out because it would lie on a path of great resistance compared to new path.

3. Bulbs A and B (below) are identical, and are both glowing. Bulb B is removed from its socket. Does the potential difference between points 1 and 2 increase, stay the same, decrease, or become zero? Explain. (cq13)

4. Bulbs A and B (below) are identical. What happens to each bulb if the switch is closed? Does it get brighter, dimmer, stay the same, or go out? Explain. (cq14)

The brightness of both bulbs will remain the same. Grounding will lower the potential but not the potential difference anywhere in the circuit.

5. The figure below shows the voltage as a function of time of a capacitor as it is discharged separately through three different resistors. Rank in order, from largest to smallest, the values of the resistances. (cq15)

6. What are the magnitude and direction of the current in the 30-ohm resistor in the figure below? Draw a graph of the potential as a function of distance traveled through the circuit, traveling cw from V=0V at the lower left corner. (ex4)

7. A typical American family uses 1000kWh of electricity a month. (ex11) a. What is the average current in the 120V power line to the house? b. On average, what is the resistance of a household?

Whichever capacitor discharges first must have the least resistance.

V

X

9

6

0

8. The corroded contacts in a lightbulb socket have 5.0Ω resistance. How much actual power is dissipated by a 100W (120V) lightbulb screwed into this socket? (ex16)

9. The voltage across the terminals of 9.0V battery is 8.5V when the battery is connected to a 20Ω load. What is the battery’s internal resistance? (ex19)

10. Determine the value of the potential at points a to d in the figure below. (ex27)

11. A 10μF capacitor initially charged to 20μC is discharged through a 1.0kΩ resistor. How long does it take to reduce the capacitor’s charge to 10 μC? (ex32)

12. The figure below shows six identical bulbs connected to an ideal battery. All the bulbs are glowing. Rank in order, from brightest to least bright, the brightness of bulbs A to F. Explain. (p37)

13. A variable resistor is connected across the terminals of a battery. The figure below shows the current in the circuit as R is varied. What are the emf and internal resistance of the battery? (p44)

14. For the circuit shown below, find the current through and the potential difference across each resistor. (p62)

15. For the circuit shown below, find the current through and the potential difference across each resistor. (p63)

16. A 12V car battery dies not so much because its voltage drops but because chemical reactions increase its internal resistance. A good battery connected with jumper cables can both start the engine and recharge the dead battery. Consider the automobile circuit below: (p68)

a. How much battery could the good battery alone drive through the starter motor?

b. How much current is the dead battery alone able o drive through the starter motor?

c. With the jumper cables attached, how much current passes through the starter motor?

d. With the jumper cables attached, how much current passes through the dead battery, and in which direction?

17. The switch shown below has been in position for a very long time. It is suddenly flipped to position b for 1.25ms, and then back to a. How much energy is dissipated by the 50Ω resistor? (cp75)

18. The capacitors shown below are charged and the switch closes at t=0s. At what time has the current in the 8Ω resistor decayed to half the value it had immediately after the switch was closed? (cp76)