Practical Skills and Experimental Techniques
Planning an investigation
State a clear aim, a testable hypothesis and the variables: independent (what you change), dependent (what you measure) and controlled (kept constant). Choose apparatus suited to the required precision, for example a micrometer for wire diameter and a top-pan balance for mass. Describe how to take readings safely and how many repeats you will make. A common trap is failing to identify a controlled variable or describing a method vaguely, such as "measure the temperature" without saying how.
Recording and processing data
Draw tables with a clear heading for each column, including the unit in the heading rather than beside every number. Record raw readings to the instrument's resolution and calculate averages, then derived quantities. Plot graphs with the independent variable on the x-axis, label axes with quantity and unit, use an even scale, and draw a line of best fit rather than joining every point. Identify anomalous results and state whether they are excluded with justification. Gradient and intercept should be interpreted in physical terms.
Safety and evaluation
Identify risks and specific precautions: goggles for heating, sand tray for hot objects, low voltage for electrical work, care with sharp or heavy apparatus. In evaluation, suggest concrete improvements: take more repeats, use a finer instrument, reduce parallax, insulate to reduce heat loss, or use a data logger. Explain how each improvement reduces uncertainty. Avoid vague answers such as "be more careful".
Worked example
To find the density of a metal block, measure mass with a balance (e.g. 54.0 g) and dimensions with a vernier caliper (e.g. 3.00 cm × 2.00 cm × 1.00 cm = 6.00 cm³). Density = 54.0/6.00 = 9.0 g/cm³. State the uncertainty in each measurement, repeat each dimension three times and average, and note that the smallest dimension gives the largest percentage uncertainty.