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Obtaining, analysing and evaluating results – WJECImproving your measuring

Under the new GCSE specifications in Wales, practical work in Science will be examined. This unit will help students to prepare for the practical examination.

Part of Biology (Single Science)Practical skills

Improving your measuring

Precision and uncertainty

Try to be more precise in your measuring. Use an instrument with a smaller resolution, and read it to the smallest reading possible.

Two rulers. Ruler A measures to the nearest milimeter. Ruler B measures to the nearest centimeter.

Ruler A will give a more precise reading and will reduce the uncertainty in your result.

An uncertainty of 1 mm in 25 mm is 4 %.

An uncertainty of 1 cm in 2.5 cm is 40 %. This is ten times bigger.

How is uncertainty calculated?

\({\%{\text{~uncertainty in reading}}}=\frac{\text{instrument resolution}\times 100\%}{\text{reading taken}}\)

The resolution is the smallest division on the instrument.

Question

What is the uncertainty of a resolution of 0.01 ml in 5.52 ml?

Question

What is the uncertainty of a resolution of 0.5 ml in 5.5 ml?