Sample Notes: Practical Skills

AS Level Physics – Paper 3: Advanced Practical Skills
Topic: Experimental Skills and Practical Assessment

Manipulation, Measurement and Observation

Successful Collection of Data

• Set up apparatus accurately without external assistance.
• Follow instructions from diagrams and written prompts, including:
  • Circuit diagrams
  • Step-by-step procedural guides
• Take enough readings to allow accurate analysis.
• Repeat measurements when necessary to increase reliability.
• Use standard lab apparatus proficiently:
  • Rulers (mm precision)
  • Vernier and digital calipers
  • Thermometers
  • Top-pan balances
  • Digital and analogue voltmeters/ammeters
  • Micrometer screw gauges
  • Stopwatches (timing multiple oscillations recommended)
  • Newton meters
• Work independently with minimum supervision. Assistance from the supervisor disqualifies from full credit for this skill.

Quality of Data

• Make accurate and consistent measurements.
• Take readings over the widest possible range within apparatus constraints.
• Ensure good distribution and spread of data points.
• Data is compared against examiner expectations or control values.
• Apparatus limitation is taken into account; focus is on user error minimization.

Presentation of Data and Observations

Tables of Results

• Prepare a complete table before collecting data.
• Include columns for raw data and calculated values.
• Use proper headings with quantity and SI unit:
  • Acceptable: I / mA, t / s
  • Unacceptable: mA alone or I mA
• Column values should be consistent in precision and format.

Recording of Data, Observations and Calculations

• Consistently record to the correct number of significant figures.
• Maintain precision suitable to the measuring instrument:
  • e.g. Use mm precision if measuring with a millimeter scale.
• Perform calculations from raw data clearly with all steps shown.
• Round calculated values to the correct significant figures:
  • Follow lowest significant figure rule from raw data (n or n+1 sig. figs.).

Graphical Work

Graph Layout

• Label axes with both variable and unit.
• Choose appropriate scale:
  • Data should occupy at least 50% of grid area on both axes.
  • Use simple multiples: 1, 2, 5 per 2 cm.
• Regular axis labeling (every 2 cm minimum).
• Use false origin if beneficial for graph clarity.

Plotting of Points

• Plot points with <1 mm precision.
• Use crosses (×) or encircled dots (⚬) to mark data points.
• Points must be easily visible and not oversized.

Trend Line

• Draw straight line of best fit or appropriate smooth curve.
• Use thin, continuous pencil lines.
• Do not include kinks or sharp angles in curves.
• Identify anomalous points if excluded (circle them or note clearly).

Analysis, Conclusions and Evaluation

Interpretation of Graph

• Match straight-line graphs to equations in the form y = mx + c.
• Use graphical data to:
  • Calculate gradients and y-intercepts
  • Extract constants
  • Identify proportional or inverse relationships
• Use at least half the line for gradient calculation.
• If intercept isn’t on the axis, calculate using equation.

Drawing Conclusions

• Use data to:
  • Validate hypotheses
  • Predict outcomes
  • Estimate physical constants
• Compare calculated constants to known values.
• Use % difference and % uncertainty to determine validity.

Estimating Uncertainties

• Estimate and state uncertainties in all raw measurements:
  • e.g. ±0.1 cm for a ruler, ±0.01 A for an ammeter.
• Express uncertainties as:
  • Absolute (e.g. ±0.2 s)
  • Percentage (e.g. ±2%)
• Use half-range rule for repeated measurements:
  • Uncertainty = (max – min) / 2

Evaluation of Method

Identifying Limitations

• Mention specific sources of uncertainty with reason.
  • e.g. “Reaction time affects stopwatch readings”
  • e.g. “Zero error in micrometer screw gauge”
• State how these affect result quality and accuracy.

Suggesting Improvements

• Propose realistic modifications:
  • Better instruments (e.g. digital timer)
  • Improved alignment of components
  • Increased number of repeats
  • More controlled environment (e.g. eliminate drafts)
• Describe changes in clear terms or labeled diagrams.
• Must be feasible in a school lab.

Common Apparatus in Paper 3

Electrical Components

• 1.5V cells, variable power supplies (0–12V)
• Rheostats, resistors, switches, connecting wires
• Digital/analogue voltmeters and ammeters
• Lamps: 6V 60mA, 2.5V 0.3A

Measuring Devices

• Top-pan balances (±0.1 g)
• Rulers, vernier calipers, micrometer screw gauges
• Thermometers (–10°C to 110°C)
• Stopwatches (±0.1s)
• Newton meters (1N, 10N)

Thermal Apparatus

• Polystyrene cups, electric kettle, beakers
• Stirrer, adhesive putty, adhesive tape

Mechanical Apparatus

• Pendulum bobs, springs (25 N/m)
• Mass hangers, slotted masses (10g to 100g)
• Pulley systems, clamps and bosses

Important Notes on Administration

• Practical exams are supervised.
• Supervisors must not assist in data processing, analysis, or evaluation.
• Details of help given must be reported to Cambridge.
• Safety regulations must be followed based on local lab protocols.

All skills are tested through two structured experiments worth 20 marks each:

• Q1: Data collection + graph + conclusions
• Q2: Data collection + conclusion + method evaluation (often inaccurate setup)