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AP PHYSICS 2
Circuits 3 Problem Set
Suppose you have a 12-V voltage source, but you need only 4 V to power the electronic
component in which you are interested.
1. Sketch a circuit that would allow you to get the desired voltage. Use standard
conventions for illustrating the voltage source and resistor(s). Label the value of the
voltage source and any resistors in your circuit.
2. Are there alternate solutions to the question above? If so, explain. If not, explain why
not.
3. If an ammeters is not to significantly alter the circuit it is measuring, what must its resistance
be?
4. If a voltmeter is not to significantly alter the circuit it is measuring, what must its resistance
be?
5. Placing capacitors in series is typically a poor choice. Why?
6. Determine the equivalent resistance of the ‘ladder’
of equal 175  resistors, i.e., what would an
ohmmeter read if it were connected to points A
and B?
Use the diagram at right to answer questions 7 – 14.
7. What is the net resistance of the circuit to the
right?
R1
R3
R5
R2
R4
R6
If each resistor is 5  and the voltage source is 10 V, complete the VIRP table.
V
I
R
P
R1
Q9b
Q9a
5
Q9c
R2
Q10a
Q10b
5
Q10c
R3
Q11b
Q11a
5
R4
Q12b
Q12a
5
R5
5
R6
5
Total
10
Q8b
Q8a
Q8c
15. Suppose you have six 4.8 F capacitors. What will their effective capacitance be if you
connect them…
a. In parallel?
b. In series?
AP Physics 2
Circuits 3 Problem Set
page 2 of 6
Suppose you place a constant voltage source between each of open terminals below.
16. In which circuit(s) (A-E) will current flow
uninterrupted? Briefly explain.
17. In which circuit(s) will current flow then
stop? Briefly explain.
18. In which circuits, if any, would current flow
through the circuit after the voltage source
were removed.
19. Suppose the resistor in circuit B were a light bulb. Sketch its brightness over time.
(t=0 when the voltage is first applied to the circuit).
Estimate the values of the resistors required to make intermittent windshield wipers:
20. One wipe every 15 seconds
21. One wipe every 4 seconds
22. One wipe every 2 seconds
AP Physics 2
Circuits 3 Problem Set
page 3 of 6
The circuit at the right has a total resistance of 15.0 k, and the
battery supplies 24.0 V. If the time constant in the circuit below is
measured to be 18.0 s,
23. calculate the total capacitance.
24. calculate how long it takes the resistor to reach 16.0 V after the switch is closed.
AP Physics 2
Circuits 3 Problem Set
page 4 of 6
In the lab, you connect a resistor and a capacitor with an unknown value in series with a battery
that supplies a voltage of 12 V. When the switch is closed at time t = 0, the circuit is
completed. Suppose you measure current through the circuit as a function of time.
𝑉
𝑡
When you plot your data, you find that 𝐼(𝑡) = 𝑅 𝑒 − ⁄4
25. Using common symbols for the battery, resistor, capacitor, and switch, draw the circuit
that you constructed. Show the circuit before the switch is closed. Include whatever
other devices you need to measure the current through the resistor to obtain the plot
above. Label each component in your diagram.
26. Determine the value of the resistor in the circuit.
27. What was the capacitance of the capacitor?
AP Physics 2
Circuits 3 Problem Set
page 5 of 6
In the circuit shown to the right, the switch S is initially in the
open position and the capacitor is initially uncharged. A graph of
the capacitor’s voltage over time is shown at right. The battery
has an emf of 20 V, the resistor R1 has a resistance of 15 k, and
the capacitor has a capacitance of 20 F.
28. Determine the voltage across resistor R2
immediately after the switch is closed.
29. Determine the voltage across resistor R2 a long time after the switch is closed.
30. Calculate the value of the resistor R2.
31. On the graph below, sketch the current in R2 has a function of time from 0 – 15 s.
Label the vertical axis with appropriate values.
AP Physics 2
Circuits 3 Problem Set
page 6 of 6