7.2 Experimental skills and investigations
- Syllabus
- 0625–2026–2027
- Topic
- 7.2
- Level
- —
Learning objectives
7.2.1Select and safely use techniques and apparatus• Demonstrate knowledge of how to select and safely use techniques, apparatus and materials, including following a sequence of instructions where appropriate.7.2.2Plan experiments and investigations• Plan experiments and investigations with suitable variables, methods, apparatus and safety controls.7.2.3Record observations and measurements• Make and record observations, measurements and estimates with appropriate precision and units.7.2.4Interpret and evaluate experimental data• Interpret and evaluate experimental observations and data, including patterns, anomalies and limitations.7.2.5Evaluate and improve methods• Evaluate experimental methods and suggest possible improvements.
Select and safely use experimental techniques and apparatus
Choose apparatus by matching its purpose, range, resolution and practical limits to the required measurement.
| Need | Selection principle |
|---|---|
| small diameter, such as wire | micrometer screw gauge gives finer resolution than a ruler |
| time interval | timer with suitable resolution and a clear start/stop event |
| electrical quantity | correct meter, range and circuit connection |
| radiation direction | shielding and collimation appropriate to the source |
Identify hazards before starting, use the stated protective controls, keep the setup stable and follow the operating sequence so that safety and measurement validity are both preserved.
Read scales at eye level where parallax is possible, check zero before measuring, place the instrument correctly and record only precision justified by the scale.
The instrument with the finest resolution is not automatically best if its range, contact method or safety constraints do not suit the measurement.
Plan a controlled physics investigation
A plan must state the relationship being tested and make clear how evidence will be collected to test it.
| Element | What to specify |
|---|---|
| independent variable | what is deliberately changed and the range/intervals |
| dependent variable | what is measured and with which instrument |
| control variables | what is kept constant and how |
| method | ordered actions, apparatus arrangement and when readings are taken |
| quality | repeats, averaging, range and enough values to reveal a trend |
| safety | hazard, resulting risk and practical control |
Where calibration is required, use known fixed values and wait for a stable reading before marking the scale—for example melting ice for 0 °C and steam above boiling water for 100 °C on a thermometer.
State how results will be processed or graphed so the planned measurements actually answer the investigation aim.
Listing apparatus is not a plan. Another learner should be able to reproduce the investigation and know which variables change, are measured and are controlled.
Make and record measurements appropriately
Record observations and measurements directly in a prepared table with each quantity named and its unit placed once in the heading.
| Measurement feature | Recording rule |
|---|---|
| analogue scale | estimate between divisions only to a justified precision |
| digital display | retain the displayed resolution unless the reading is unstable |
| repeated readings | keep consistent decimal places, identify anomalies and calculate a mean when appropriate |
| calculated value | use guard digits, then round to sensible significant figures |
For a uniform thermometer scale, use the fraction of the distance between the 0 °C and 100 °C fixed points. If the liquid is 8 mm below 0 °C and extends 64 mm above 0 °C while the fixed-point separation is 80 mm, the indicated temperature is (64/80) × 100 = 80 °C.
Qualitative observations also need precise language: record colour, motion, sound or state changes without adding an explanation to the observation column.
More decimal places do not create greater accuracy. Precision must reflect instrument resolution and measurement conditions.
Interpret and evaluate experimental observations and data
Interpretation turns observations into a supported pattern or relationship; evaluation judges how strongly the method and data support that interpretation.
| Check | Evidence to inspect |
|---|---|
| pattern | direction, shape, gradient or proportionality |
| anomalies | points that depart from the overall pattern and possible reasons |
| repeatability | spread among repeats and stability of the mean |
| uncertainty | scale resolution, reaction time, reading range and relative uncertainty |
| validity | whether controls and method isolate the intended relationship |
| limitations | restricted range, systematic effects or assumptions |
Use a best-fit line or curve to judge the overall relationship rather than joining points dot-to-dot. A scattered point should be investigated, not silently deleted.
A conclusion should state the supported relationship and its range, then acknowledge any limitation that materially weakens it.
Agreement with an expected value does not by itself prove a method is valid, and an anomalous point does not automatically invalidate the whole dataset.
Evaluate and improve an experimental method
A useful method evaluation identifies a specific weakness, explains how it affects the result and proposes a practical change that directly reduces that effect.
| Limitation | Likely effect | Targeted improvement |
|---|---|---|
| energy lost to surroundings | supplied energy is not all transferred to the intended object | insulate, use a lid, reduce transfer time or account for apparatus heating |
| reaction-time timing | random spread or systematic start/stop delay | use electronic sensing or time many cycles |
| parallax on a scale | reading shifted by viewing angle | read perpendicular to the scale or use a fiducial marker |
| too few values | trend poorly defined | use more values over a wider safe range |
Repeats reduce random uncertainty and help reveal anomalies; they do not remove a systematic zero error or heat loss.
Where possible, state the direction of bias. If energy lost to the surroundings is wrongly treated as heating the sample, a calculated specific heat capacity may be too high.
'Use better equipment' is not an actionable improvement. Name the equipment or change and explain which limitation it reduces.