AP Physics 2 · Exam guide
AP Physics 2 Experimental Design Explained: Planning an Experiment and Analyzing the Data
AP Physics 2 free-response questions can ask you to plan an experiment, for example to find a resistance, an index of refraction or the temperature change of a sample. The plan is scored on the same elements each time: variables, equipment, procedure and analysis. The data below are made up for practice.
What a strong plan includes
| Element | What to write |
|---|---|
| Relationship | The equation connecting what you want to the quantities you can measure. |
| Variables | What you change, what you measure, and what stays the same. |
| Equipment | Each device and what it measures, such as a voltmeter in parallel and an ammeter in series. |
| Procedure | Steps another person could repeat, with several settings and repeated trials. |
| Analysis | A graph that is a straight line, with the slope or intercept giving the quantity you want. |
A worked example: finding a resistance
Goal: find the resistance R of an unmarked resistor. The relationship is Ohm's law, \(V = IR\).
- Independent variable: the battery voltage V, changed in steps with a variable power supply.
- Dependent variable: the current I through the resistor.
- Constant: the same resistor, at the same temperature (allow it to cool between readings).
- Equipment: a variable power supply, the resistor, an ammeter in series, a voltmeter in parallel across the resistor, and wires.
- Procedure: set five voltages, record V and I at each, and repeat each setting twice.
Made-up results:
| Voltage V (V) | Current I (A) |
|---|---|
| 2.0 | 0.10 |
| 4.0 | 0.20 |
| 6.0 | 0.30 |
| 8.0 | 0.40 |
| 10.0 | 0.50 |
Graph I on the vertical axis against V on the horizontal axis. The points fall on a line through the origin, with slope \(\Delta I / \Delta V = 0.40 / 8.0 = 0.050\) A/V, which equals \(1/R\). So \(R = 1/0.050 = 20\ \Omega\).
It gives one setting, no graph and no way to find R from several readings.
It names the equipment and its placement, uses several settings, and explains the analysis.
Common mistakes
- Placing a voltmeter in series or an ammeter in parallel.
- Taking a single reading instead of several settings.
- Forgetting that the slope may be 1/R, not R, and reporting the wrong quantity.
- Leaving out the units of the answer.
Frequently asked questions
Does AP Physics 2 have an experimental design question?
Free-response questions can ask you to plan an experiment, and the habits are the same as for the Physics 1 version.
Why use a graph instead of one measurement?
A graph uses all your data and shows whether the relationship is really linear, which a single measurement cannot.
What if my graph would not be a straight line?
Choose what to plot so the relationship is linear, such as plotting one quantity against the reciprocal of another.
How do I place meters in a circuit?
An ammeter goes in series with the part being measured, and a voltmeter goes in parallel across it.
Where can I find the official scoring rules?
Exam formats change a little from year to year, so check the current course and exam description on the College Board site before test day.
Keep practicing
Every lesson in the AP Physics 2 course ends with practice items and an Exam focus box, and every unit has a ten-question practice set with worked answers. These free lessons also build the skills the free-response section tests:
See the AP Physics 2 course Free lessons and lesson list
Other free-response guides:
- AP Physics 2 FRQ Guide: Free-Response Habits for Circuits, Gases, Optics and Modern Physics
- AP Physics 2 Thermodynamics FRQ Explained: PV Diagrams and the First Law
AP is a registered trademark of the College Board, which is not affiliated with and does not endorse this site. This guide is our own explanation of the question types and scoring. For the official scoring guidelines, see the College Board.