Practical Skills I: Processing Results

Revise Practical Skills I: Processing Results for Physics 3 (IAL) WPH13 (AS Level) — revision notes and instant AI marking.

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Edexcel IAL Physics · Practical Skills I

Processing Results

The Big Idea: Collecting data is only half the job — a good physicist processes it carefully: calculating averages, plotting honest graphs, spotting relationships between variables, minimising errors, and always attaching an honest uncertainty to every number.

Summary OverviewThe whole chapter in one scroll

Calculations: leave space in tables for means and derived quantities (like extension or area) that can't be measured directly.
Graphs: pick sensible scales that fill at least half the grid, label axes with quantity and unit using a forward slash, plot points to within half a small square, and draw a smooth line/curve of best fit (not forced through the origin).
Units: everything reduces to 7 SI base units (kg, m, s, A, K, mol, cd); other units like N, J, Pa are "derived" from these using their defining equations.
Relationships: directly proportional (y ∝ x, straight line through origin) vs inversely proportional (y ∝ 1/x, decreasing curve) vs inverse square law (y ∝ 1/x²).
Gradients: calculated from a large triangle drawn on the line of best fit — never from two raw data points, and never a tiny triangle.
Reducing errors: watch for parallax error, missing fiducial markers, zero errors, poor-resolution equipment, and unwanted heating effects.
Improvements: data loggers, cameras, and computer modelling reduce human error and improve reproducibility.
Uncertainty: can be absolute, fractional, or percentage — and there are specific rules for combining uncertainties when adding, multiplying, or raising to a power.

1. Calculations Using Experimental Data

Why raw data isn't enough

Think of an experiment in two stages: collecting the raw numbers, and then processing them into something useful. A table full of raw readings tells you almost nothing on its own — you need to turn it into means, calculated quantities, and eventually graphs. That's what this whole chapter is about.

The golden rule when designing a data table: always leave space for calculations. If you're taking three repeat current readings, leave a column for the average. If you need "extension," which can't be measured directly, leave columns for initial length, final length, and the calculated extension.

The Mean

Formula

Mean = (sum of the readings) ÷ (number of readings)

In plain English: add up all your repeat readings, then divide by how many readings you took.

Any anomalous (clearly wrong/outlier) readings should be ignored before calculating the mean.
The mean must be given to the same number of significant figures as the individual readings used to calculate it — don't suddenly gain precision you don't actually have!