Overview
This lecture explains how to estimate measurement uncertainty using two main methods and highlights their use in A-level practical exams.
Estimating Uncertainty with Multiple Readings
- When measuring a quantity multiple times, estimate uncertainty using "half the range" of the values.
- Half the range is calculated as (Maximum value - Minimum value) divided by 2.
- This value represents the absolute uncertainty and is expressed in the same units as the measurement.
- To report results, write the average value ± the calculated uncertainty (e.g., 2.50 ± 0.02 cm).
- This method is commonly used in Paper 3 and Paper 5 practical exams.
Limitations of Half the Range Method
- If using half the range gives an uncertainty of zero, this method cannot be used.
Estimating Uncertainty with a Single Reading
- If only one reading is possible, estimate uncertainty based on the instrument's smallest reading or reasonable judgment.
- For example, with a ruler measuring to 0.1 cm, uncertainty might be estimated as 0.1 cm or a slightly higher value if the object is irregular or soft.
- This estimation is mostly used in Paper 3 practical exams.
- Over time, experience and reviewing past papers will help improve estimation skills.
Reporting Measurements with Uncertainty
- Measurements should be reported as: average value ± absolute uncertainty, with units given once at the end.
Key Terms & Definitions
- Uncertainty — An estimate of how much a measured or calculated value might vary.
- Absolute Uncertainty — The margin of doubt, given in the same units as the measurement.
- Half the Range — (Maximum reading - Minimum reading) ÷ 2, used to estimate uncertainty with multiple measurements.
Action Items / Next Steps
- Practice using both methods to estimate uncertainty in experiments.
- Review past exam questions to familiarize yourself with acceptable uncertainty estimates.
- Prepare for next lesson on interpreting uncertainty and assessing data validity.