Year 8 Science · Unit 4 · Lesson 8

Accuracy, Precision and Reliability

Challenge Worksheet

Name

Date

Class

Learning Goals

Interpret a dot-cluster diagram to classify measurement quality as accurate, precise, both or neither.
Design a method for measuring boiling point of seawater that maximises both accuracy and precision.
Explain calibration, trial number, systematic error identification, and significant figures in the context of a real experiment.

Warm Up

Read the graph

Four students each threw 5 darts at a target. Each student's results are shown in the dot-cluster diagrams below. The bullseye = the true value (100 points). Answer the three questions that follow.

Student A

Student B

Student C

Student D

(a) Complete this table classifying each student. Write "Yes" or "No" in each cell and identify the type of error (random, systematic, or none).

Challenge 4 marks

Student	Accurate?	Precise?	Main error type
A
B
C
D

(b) Student A is the most consistent thrower but consistently misses the centre. What change to their technique or equipment would improve accuracy without reducing precision?

Challenge 2 marks

Go Deeper

Design challenge

A student wants to accurately and precisely measure the boiling point of seawater. The accepted value is approximately 102°C (slightly higher than pure water due to dissolved salts). The student has a standard laboratory thermometer, a Bunsen burner, a 250 mL beaker and access to a calibration reference of 100°C (boiling pure distilled water).

(a) Describe a calibration step the student should perform before measuring the seawater. Why does this step help achieve accuracy rather than just precision?

Challenge 3 marks

(b) How many trials should the student perform to achieve reliable results? Explain what reliability means and what calculating the mean and range of repeated trials tells you.

Challenge 3 marks

(c) After 5 trials, the student finds all readings are consistently 1.5°C too low (e.g. 100.5°C instead of ~102°C). What type of error is this, and what should the student do to find and fix it? Would repeating trials 10 more times solve the problem?

Challenge 3 marks

(d) The student's final 5 corrected readings are: 102.1°C, 101.9°C, 102.0°C, 102.2°C, 101.8°C. Report the final result to the correct number of significant figures and state whether the results are accurate, precise, or both. Justify with the data.

Challenge 3 marks

Wrap Up

In one sentence, what was the main idea of this lesson?