Errors and uncertainties
Cambridge A-Level Physics (9702) · Unit 1: Physical quantities and units · 8 flashcards
Errors and uncertainties is topic 1.3 in the Cambridge A-Level Physics (9702) syllabus , positioned in Unit 1 — Physical quantities and units , alongside Physical quantities, SI units and Scalars and vectors. In one line: A systematic error is a consistent error that affects all readings in the same way, shifting them from the true value in a consistent direction.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 8 flashcards — 2 definitions, 3 key concepts and 3 calculations — covering the precise wording mark schemes reward. Use the 2 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
'systematic error' and provide an example
A systematic error is a consistent error that affects all readings in the same way, shifting them from the true value in a consistent direction.
What the Cambridge 9702 syllabus says
2025-2027 syllabus, in our words · AS LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Understand and explain how measurements are affected by random errors and by systematic errors, zero errors included.
- Understand how precision differs from accuracy.
- Work out the uncertainty in a quantity calculated from measurements by simply adding absolute uncertainties or percentage uncertainties.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9702 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Errors and uncertainties
- › When a quantity is raised to a power 'n', multiply its percentage uncertainty by 'n' when calculating the total percentage uncertainty.
Define 'systematic error' and provide an example.
A systematic error is a consistent error that affects all readings in the same way, shifting them from the true value in a consistent direction.
Define 'random error' and provide an example.
A random error is an unpredictable error that affects readings inconsistently, causing them to be scattered around the true value.
Explain the difference between accuracy and precision.
Accuracy refers to how close a measurement is to the true value. Precision refers to the repeatability of a measurement; how close multiple measurements are to each other, regardless of the true value.
A voltmeter consistently reads 0.2V too high. What type of error is this, and how does it affect accuracy and precision?
This is a systematic error (specifically, a zero error). It affects the accuracy of the measurements, making them consistently inaccurate. It does not directly affect the precision, as the measurements are still repeatable with the same offset.
How do you combine absolute uncertainties when adding or subtracting measurements?
When adding or subtracting measurements, the absolute uncertainties are added together. For
How do you combine percentage uncertainties when multiplying or dividing measurements?
When multiplying or dividing measurements, the percentage uncertainties are added together. For
A student measures a length as 2.5 ± 0.1 cm and a width as 1.2 ± 0.1 cm. Calculate the area and its absolute uncertainty.
Area = 2.5 * 1.2 = 3.0 cm². Percentage uncertainty in length = (0.1/2.5)*100 = 4%. Percentage uncertainty in width = (0.1/1.2)*100 = 8.33%. Total percentage uncertainty in area = 4 + 8.33 = 12.33%. Absolute uncertainty in area = (12.33/100) * 3.0 = 0.37 cm². Therefore, area = 3.0 ± 0.4 cm² (rounded to 1 sf).
Describe how repeated measurements can help reduce the impact of random errors.
Taking multiple measurements and calculating the average helps to reduce the impact of random errors. Random errors tend to cancel each other out when averaged, providing a more accurate estimate of the true value.
Review the material
Read full revision notes on Errors and uncertainties — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 1 — Physical quantities and units
Errors and uncertainties sits alongside these A-Level Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Errors and uncertainties deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
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