AP Physics C: Electricity & Magnetism 11.5 Compound Direct Current Circuits Questions

2 points
For selecting "It is the same through both." 1 point For a correct justification 1 point

Example: The sample of wire and the resistor are in series with each other and therefore will have the same current. Note: Because the voltmeter is ideal, it will have no effect on the result. No points are earned if the wrong answer is selected.

2 points
For selecting "It will depend on the resistance of the sample." 1 point For a correct justification including argument using Ohm's law, voltage drop 1 point across resistors, etc. Example: Because the sample of wire has resistance, it cannot be known whether the wire of the resistor has the greatest resistance and which has the higher potential difference across it. Therefore, it will depend on the resistance of the wire sample. No points are earned if the wrong answer is selected.

1 point
For indicating the correct quantities for each axis Horizontal axis: $I_{R}$ Vertical axis: $V_{r}=\boldsymbol{\varepsilon}-V_{R}$ Note: Credit is received if the axes are reversed.

3 points

For a correct scale that uses more than half the grid and for correctly labeling the 1 point axes including units
For correctly plotting given data 1 point
For drawing a straight line consistent with the given data 1 point

2 points
For correctly calculating slope using the best-fit straight line and not data points 1 point slope $=\frac{\left(V_{2}-V_{1}\right)}{\left(I_{2}-I_{1}\right)}=\frac{(0.30-0.10) \mathrm{V}}{(0.60-0.22) \mathrm{A}}=0.526 \mathrm{~V} / \mathrm{A}$
Note: Linear regression gives slope $=0.485 \mathrm{~V} / \mathrm{A}$. (Student must indicate that the value comes from a linear regression from the calculator, and the equation of the line must be present.)
For correctly relating r to the slope 1 point
$V_{r}=I_{R} r$, therefore the slope equals r
$r=0.526 \Omega$
Note: Linear regression gives $r=0.485 \Omega$.

2 points
For selecting "Less than" with an attempt at a justification For a correct justification Example: The resistance calculated from the graph is the sum of the sample resistance plus the ammeter resistance because it is not ideal. The actual resistance is the calculated resistance minus the ammeter resistance, and therefore less than the calculated resistance. No points are earned if the wrong answer is selected.

2 points
For selecting "Greater than" with an attempt at a justification For a correct justification Example: If the voltmeter is not ideal, that would add an additional resistor in parallel. A parallel resistor reduces the total resistance of the circuit. This would lead to an increase in current and a higher reading on the ammeter. No points are earned if the wrong answer is selected.

For correctly placing the voltmeter in parallel with Resistor A, Resistor B, or the combination of resistors A and B

Example Response

1 point

For selecting $\left|\Delta V_{2}\right|<\left|\Delta V_{1}\right|$ with an attempt at a relevant justification For indicating that the total resistance has increased For indicating that the current decreases due to the increased resistance 1 point

OR

For indicating that the potential difference across the inductor will increase, and, therefore, the potential difference across $\mathrm{R}_{\mathrm{A}}$ must decrease

Example Response
$\left|\Delta V_{2}\right|<\left|\Delta V_{1}\right|$, because the inductor has nonnegligible resistance, and the total resistance of the new circuit increases as compared to the original circuit. Therefore, the current in the new circuit is reduced compared to that of the original circuit when steady-state conditions are established.

OR
$\left|\Delta V_{2}\right|<\left|\Delta V_{1}\right|$, because the inductor has nonnegligible resistance, and the total resistance of the new circuit increases as compared to the original circuit. Therefore, the potential difference across the inductor increases, which decreases the potential difference across $\mathrm{R}_{\mathrm{A}}$ compared to that of the original circuit when steady-state conditions are established.

Total for part (d)

for question 2

15 points