AP Physics 2- 11.1 Electric Current- Exam Style questions - FRQs- New Syllabus

(a)
Connect the power source, resistor, and bulb in series. Place one ammeter in series before the bulb and a second ammeter in series after the bulb. Connect the voltmeter in parallel across the bulb.

Measure the current entering the bulb, \(I_{\text{in}}\), with one ammeter. Measure the current leaving the bulb, \(I_{\text{out}}\), with the other ammeter. Measure the potential difference across the bulb, \(\Delta V_{\text{bulb}}\), with the voltmeter.

The two ammeters allow the students to test whether current is used up in the bulb. The voltmeter allows the students to test whether charges lose electric potential energy while passing through the bulb.

(b)(i)
Compare \(I_{\text{in}}\) and \(I_{\text{out}}\).

If \(I_{\text{in}}=I_{\text{out}}\), then the number of electrons per second entering the bulb is equal to the number of electrons per second leaving the bulb. Therefore, current is not used up in the bulb.

This agrees with conservation of charge. Charge flows through the bulb, but the bulb does not consume charge.

(b)(ii)
Use the voltmeter reading across the bulb.

If \(\Delta V_{\text{bulb}}\neq 0\), then electrons change electric potential while moving through the bulb. The change in electric potential energy is related to potential difference by

\(\Delta U_E=q\Delta V_{\text{bulb}}\)

Thus, a nonzero \(\Delta V_{\text{bulb}}\) means the electrons transfer energy to the bulb, where the energy is transformed mostly into thermal energy and light.

(c)(i)
No major change is required. The same setup can be used to test whether the bulb is nonohmic.

One ammeter could be removed because the current entering and leaving the bulb should be the same, but keeping both ammeters does not prevent the experiment from working.

(c)(ii)
Collect additional data by changing the setting of the adjustable power supply. For each setting, measure the current through the bulb \(I\) and the potential difference across the bulb \(\Delta V_{\text{bulb}}\).

Multiple pairs of \(I\) and \(\Delta V_{\text{bulb}}\) are needed to determine whether the resistance stays constant as current changes.

(d)
Make a graph of \(I\) as a function of \(\Delta V_{\text{bulb}}\), or make a graph of \(\Delta V_{\text{bulb}}\) as a function of \(I\).

If the bulb is ohmic, then the data should be linear because

\(\Delta V_{\text{bulb}}=IR\)

For an ohmic bulb, \(R\) is constant, so the ratio

\(R=\dfrac{\Delta V_{\text{bulb}}}{I}\)

should remain constant for different currents.

If the graph is clearly curved, or if the ratio \(\dfrac{\Delta V_{\text{bulb}}}{I}\) changes more than can be explained by measurement uncertainty, then the bulb is nonohmic.

The voltmeter uncertainty is about \(\pm 0.05\text{ V}\), and the ammeter uncertainty is about \(\pm 0.005\text{ A}\), based on the smallest markings. The students should include uncertainty bars on the graph. If a straight best-fit line cannot reasonably pass through the uncertainty ranges of the data points, then the data support the conclusion that the bulb is nonohmic.