How to Revise Practical Skills for IGCSE Physics

Paper 6 (Alternative to Practical) tests your ability to handle experimental data, draw conclusions, and evaluate methods. It is worth 20% of your final grade.

What Paper 6 tests

The paper has four main skill areas:

1. Planning: designing an experiment to test a hypothesis.
2. Collecting data: reading instruments, recording values, making measurements.
3. Presenting data: drawing tables, plotting graphs, calculating quantities.
4. Analysis and evaluation: drawing conclusions, identifying sources of error, suggesting improvements.

Tables

When recording data in a table:

• Column headings must include the quantity and the unit (e.g., “Length / cm”).
• All values in a column must be recorded to the same number of decimal places.
• Calculated values must be shown to an appropriate number of significant figures (no more than the raw data).

Graphs

Graph marks are awarded for:

• Correct axis labels with units.
• Sensible scales that use at least half the available grid.
• Accurately plotted points (within half a small square).
• A best-fit line (straight line or smooth curve, not dot-to-dot).

Gradient calculations

When asked to find the gradient:

1. Choose two points on the line of best fit (not data points), far apart.
2. Draw a large triangle.
3. Read the coordinates carefully.
4. Calculate: gradient = (y2 minus y1) / (x2 minus x1).
5. Include the unit.

Show your working on the graph with clearly marked lines.

Sources of error

Common sources of error in physics experiments:

• Parallax error when reading a scale (eye not at the correct angle).
• Reaction time when using a stopwatch.
• Heat loss to the surroundings in thermal experiments.
• Friction in mechanics experiments.
• Zero error on measuring instruments.

For each error, state how it can be reduced (e.g., use a fiducial marker to reduce parallax, repeat and average to reduce random errors).

Precision vs accuracy

Precision: how close repeated measurements are to each other. Improved by reducing random errors (e.g., averaging).

Accuracy: how close a measurement is to the true value. Improved by reducing systematic errors (e.g., calibrating instruments, correcting for zero error).

Planning experiments

When asked to plan an experiment:

1. State what you would measure (independent and dependent variables).
2. State what you would keep constant (control variables).
3. Describe the method step by step.
4. State the measuring instruments you would use and why.
5. Explain how you would make the results reliable (e.g., repeat and average).