# Practical skills (AS)

> CIE A-Level Physics · CIE 9702 AS Level
> Source: https://www.owlsprep.com/study/cie-9702-u15-overview/
> Weight: n/a

This unit covers all core practical skills assessed in CIE 9702 AS Level Paper 3, following the full workflow of an experiment from planning to evaluation, building a foundation for A2 practical work.

**Prerequisites:** Completion of all AS Level theory units (Units 1-4) of CIE 9702 Physics

## Learning objectives

- Plan valid, testable physics experiments aligned with CIE marking criteria
- Record accurate measurements and observations using standard laboratory equipment
- Process and analyse experimental data graphically and numerically
- Calculate, propagate and interpret measurement uncertainties correctly
- Evaluate experimental limitations and suggest specific, realistic improvements

## Unit at a glance

This unit follows the natural sequence of conducting a physics experiment, matching the structure of CIE AS Paper 3 assessment. We start with designing a valid experiment, move through making accurate measurements, processing and analysing data, accounting for uncertainty, and end with evaluating procedures to identify improvements. Each sub-topic directly maps to the marking criteria you will encounter on your exam.

All core sub-topics for this unit are listed below:
- [Experiment planning](https://www.owlsprep.com/study/cie-9702-u15-experiment-planning/) — Learn to define variables, write testable hypotheses, and design valid experimental procedures for assessment.
- [Measurement and observation](https://www.owlsprep.com/study/cie-9702-u15-measurement-and-observation/) — Master correct use of common lab equipment and how to record clear, accurate measurements.
- [Data analysis](https://www.owlsprep.com/study/cie-9702-u15-data-analysis/) — Process raw data, plot linear graphs, and calculate unknown quantities from graphical results.
- [Uncertainty analysis](https://www.owlsprep.com/study/cie-9702-u15-uncertainty-analysis/) — Calculate absolute, fractional and percentage uncertainty, and propagate uncertainty through calculations.
- [Evaluation of results](https://www.owlsprep.com/study/cie-9702-u15-evaluation-of-results/) — Identify experimental limitations and suggest specific, relevant improvements to procedure.

## Common pitfalls

- **Wrong:** Writing vague improvements like 'be more careful' or 'use better equipment'
  - Why it fails: Examiners require specific improvements that directly address the source of error
  - Correct: Explain how changing a specific step reduces error, e.g. 'use a vernier calliper instead of a metre rule to reduce length uncertainty'
- **Wrong:** Forgetting to label graph axes with units, or using uneven scales
  - Why it fails: These common easy-to-avoid errors lose multiple easy marks in data analysis
  - Correct: Always check axes for labels, units and even linear spacing before plotting points
- **Wrong:** Confusing independent and dependent variables in planning
  - Why it fails: This invalidates your entire procedure and loses most planning marks
  - Correct: Remember: independent = what you change, dependent = what you measure

## Cheatsheet

| Concept / Formula | Description |
| --- | --- |
| Percentage Uncertainty | $\frac{\text{absolute uncertainty}}{\text{measured value}} \times 100\%$ |
| Uncertainty in Gradient | $m_{\text{max}} - m_{\text{min}}$ |
| Linear Graph Form | $y = mx + c$ (where $m$ = gradient, $c$ = y-intercept) |
| Random Error | Unpredictable variation between measurements, reduced by repeated readings |
| Systematic Error | Consistent offset in readings, caused by uncalibrated equipment |
| Independent Variable | Variable manipulated/changed by the experimenter |
| Dependent Variable | Variable measured by the experimenter, responds to changes in IV |

## What's next

Start with the first sub-topic of this unit to build your practical skills in the same order they appear on AS Paper 3. Once you complete all sub-topics here, you can move on to the A2 Level practical skills unit to extend your knowledge for the full A-Level qualification.

- [Experiment planning](https://www.owlsprep.com/study/cie-9702-u15-experiment-planning/)
- [Practical skills (A2)](https://www.owlsprep.com/study/cie-9702-u16-overview/)
- [Measurement and Observation](https://www.owlsprep.com/study/cie-9702-u15-measurement-and-observation/)

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