# Delve AP Physics C Quiz 6

The copy of the test used in class is available, with the multiple choice and free response sections separate.

## Multiple Choice

- A circuit consists of a capacitor, a battery, and a resistor in
series. As a dielectric is slowly inserted into the capacitor:
- The voltage across the capacitor increases
- The voltage across the capacitor decreases
- The charge on each plate of the capacitor increases
- The charge on each plate of the capacitor decreases
- Neither the voltage nor charge changes

- Which of the following parallel-plate capacitors has highest
capacitance?
- Plates of area \(A\), separated by distance \(d\), and filled with dielectric of constant \(k\).
- Plates of area \(2A\), separated by distance \(3d\), and filled with dielectric of constant \(\frac43 k\).
- Plates of area \(A/2\), separated by distance \(d/2\), and filled with dielectric of constant \(5k\).
- Plates of area \(3A\), separated by distance \(d/4\), and filled with dielectric of constant \(k/10\).
- Plates of area \(\frac32 A\), separated by distance \(3 d\), and filled with dielectric of constant \(2 k\).

- A circuit contains a \(10 V\) battery, a \(3 \Omega\) resistor, and a \(1 \mu
F\) capacitor; how much energy is eventually stored in the
capacitor?
- \(10 \mu J\)
- \(25 \mu J\)
- \(50 \mu J\)
- \(100 \mu J\)
- \(250 \mu J\)

- What is the time constant \(\tau\) of the capacitor from Problem 3?
- \(1 \mu s\)
- \(3 \mu s\)
- \(10 \mu s\)
- \(30 \mu s\)
- \(100 \mu s\)

- How much energy is stored in the capacitor from Problem 3 after \(\tau\)
time has passed?
- \(4.0 \mu J\)
- \(6.3 \mu J\)
- \(15.8 \mu J\)
- \(19.8 \mu J\)
- \(31.5 \mu J\)

- An inductor contains a uniform magnetic field of \(0.4 mT\). What is
the energy density inside the inductor?
- \(2.51 \cdot 10^{-10} \cdot J m^{-3}\)
- \(0.064 \cdot J m^{-3}\)
- \(0.127 \cdot J m^{-3}\)
- \(159 \cdot J m^{-3}\)
- \(318 \cdot J m^{-3}\)

- Which of the following must make a capacitor discharge slower?
- Decreasing resistance and decreasing capacitance
- Increasing resistance and decreasing capacitance
- Decreasing resistance and increasing capacitance
- Increasing resistance and increasing capacitance
- None of the above

- You have four \(1 \mu F\) capacitors, which you can arrange in a
circuit. Which of the following effective capacitances can this
circuit
*not*have?- \(4 \mu F\)
- \(\frac52 \mu F\)
- \(\frac43 \mu F\)
- \(1 \mu F\)
- \(\frac12 \mu F\)

- A inductor is made of a large solenoid with length \(l\) and \(n\)
turns. Which of the following changes must decrease the inductance
\(L\) of the inductor?
- Decreasing the length and decreasing the number of turns
- Decreasing the length and increasing the number of turns
- Increasing the length and decreasing the number of turns
- Increasing the length and increasing the number of turns
- None of these changes are guaranteed to decrease the inductance

- Which of the following series circuits has the most current
flowing through it after \(1 s\), if a \(1 V\) battery is attached?
- \(1 \Omega\) resistor, \(1 F\) capacitor
- \(2 \Omega\) resistor, \(\frac13 F\) capacitor
- \(1 \Omega\) resistor, \(1 h\) inductor
- \(2 \Omega\) resistor, \(\frac13 h\) inductor
- \(2 \Omega\) resistor

- A \(1 h\), \(3 h\), and \(5 h\) inductor are placed in parallel. What
is their effective resistance?
- \(0.50 h\)
- \(0.65 h\)
- \(1.0 h\)
- \(4.0 h\)
- \(9.0 h\)

- A \(1 h\), \(3 h\), and \(5 h\) inductor are placed in series. What is
their effective resistance?
- \(0.50 h\)
- \(0.65 h\)
- \(1.0 h\)
- \(4.0 h\)
- \(9.0 h\)

- When placed in series, two inductors combine to produce a greater
effective inductance. Why is this?
- The new inductor has greater length
- The new inductor has greater cross-sectional area
- The new inductor has lesser length
- The new inductor has lesser cross-sectional area
- Two inductors in series actually produce lesser effective inductance

- When placed in parallel, two capacitors combine to produce a greater
effective capacitance. Why is this?
- The new capacitance has greater separation
- The new capacitance has greater cross-sectional area
- The new capacitance has lesser separation
- The new capacitance has lesser cross-sectional area
- Two capacitors in parallel actually produce lesser effective capacitance

- Compare the eventual behavior of the capacitor and inductor in an
RC or RL circuit:
- The capacitor eventually behaves like a large resistor, and so does the inductor
- The capacitor eventually behaves like a large resistor, the inductor like a wire.
- The capacitor eventually behaves like a wire, the inductor like a large resistor
- The capacitor eventually behaves like a wire, and so does the inductor
- The capacitor and inductor do not reach a steady state, instead oscillating in effective resistance

- As time passes, the effective resistance of a capacitor increases:
- Inverse-squared
- Inversely
- Linearly
- Quadratically
- Exponentially

- If an inductor and charged capacitor are linked in a loop, the
current in the loop will:
- Increase linearly with time
- Decrease linearly with time
- Decrease inversely with time
- Increase exponentially with time
- Oscillate

- Two inductors are placed very close to one another in parallel.
The resulting inductance is a bit larger than what one would
expect. Why?
- The charges moving in the wire are attracted to one another
- The magnetic fields interfere
- The mutual inductance of the two wires must be factored in
- The inductors deform slightly due to the presence of another inductor
- There is no reason for this; the result must be measurement error

- Which of the following is a
*not*use for inductors?- Reduce surges in a circuit
- Store energy for later release
- Transfer current between unconnected circuits
- Generate heat in heating elements
- Filter some frequencies from a signal

- When an RL circuit is switched on, the current flow is initially
zero, but slowly increases. Which of the following do
*not*affect the percentage of the final current that is flowing after \(1s\)?- The voltage
- The inductance
- The resistance
- The ratio of inductance to resistance
- The product of inductance and resistance

- Which of these describe how a capacitor acts?
- A capacitor starts off allowing current flow, and as it charges it allows increased current flow
- A capacitor starts off preventing current flow, but as it charges it allows increased current flow
- A capacitor starts off allowing current flow, but as it charges it decreases current flow
- A capacitor starts off preventing current flow, and as it charges it continues doing so
- None of the above

- How much power does a \(1 h\) inductor store when connected to a
\(3V\) battery and a \(1 \Omega\) resistor?
- \(1 J\)
- \(1.5 J\)
- \(3 J\)
- \(4.5 J\)
- \(9 J\)

- An ideal inductor is one which:
- Has maximal resistance
- Has maximal inductance
- Has maximal capacitance
- Has maximal ratio of resistance to inductance
- Has minimal resistance and capacitance

- If the time constant of an RC circuit is \(1 s\), how many seconds
must pass before the capacitor is $\frac23$-charged?
- \(0.33 s\)
- \(0.41 s\)
- \(0.67 s\)
- \(1.1 s\)
- \(1.5 s\)

- Where is the energy of an inductor stored?
- In the charges flowing through its wires
- In its geometric shape
- In the current flowing though it
- In the heat it generates
- In the field inside it

## Free Response

## Solutions

### Multiple Choice

1-10 | D | D | C | D | D | B | D | E | A | D |

11-20 | B | E | A | B | B | E | E | C | D | A |

21-25 | E | D | E | D | E |