Physics Instruction, Laboratory Safety, and Assessment
What this domain tests
Professional knowledge: planning and teaching physics practicals, running a safe laboratory, and assessing learners validly - including marking, error analysis and feedback.
Core rules
- A practical needs a clear aim, a prediction, identified variables (independent, dependent, controlled), a repeatable method, a results table with units in the headers, and an evaluation.
- Graphs: dependent variable on the y-axis, axes labelled with quantity and unit, sensible scale, line of best fit showing the trend - not dot-to-dot.
- Reliability comes from repeats and averaging; validity means the experiment measures what it claims to measure.
- Systematic errors shift every reading the same way (zero error, miscalibration); random errors scatter and are reduced by averaging.
- Safety: know the fire extinguisher, first-aid box and emergency switch; never point a laser at anyone; handle radioactive sources with tongs, store them in a lead-lined box and minimise time and distance; contain mercury spills on a tray; use low-voltage supplies and dry hands for electrical work.
Worked example
Learners measure g with a simple pendulum. Weakness: timing a single swing by hand gives a large random error. Improvement: time 20 oscillations and divide by 20, repeat three times, then plot T² against L and take g = 4π²/gradient. Reasoning: timing many oscillations divides the reaction-time error by 20, while the graph averages scatter and tests proportionality.
Traps that cost marks
- Writing a method that omits repeats or fails to control variables.
- Awarding full marks to a correct number with no unit, or to a graph with unlabelled axes.
- Treating a systematic error as something averaging will remove.
- Leaving safety out of the plan and mentioning it only when prompted.