Year 7 Science · Unit 4 · Lesson 4
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Learning Goals
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. A measuring cylinder measures the mass of a liquid in grams.
Correct it:
2. A digital instrument is always more accurate than an analog one.
Correct it:
3. A tape measure is a better choice than a 30 cm ruler for measuring the length of a classroom.
Correct it:
4. Sensitivity means the smallest to the largest value an instrument can measure.
Correct it:
5. Pure water freezes at 0 °C and boils at 100 °C.
Correct it:
Choose the right instrument
For each job, write the instrument you would use and the unit you would record. Choose from ruler, measuring cylinder, balance, thermometer and stopwatch. Each instrument is used once.
| Measuring job | Instrument | Unit |
|---|---|---|
| How tall a bean plant has grown | ||
| How much water to pour into a beaker for an experiment | ||
| How long a trolley takes to roll down a ramp | ||
| How hot a cup of tea is | ||
| The mass of a handful of marbles |
Order the steps: measuring 60 mL of water
Number the steps from 1 (first) to 5 (last).
| Step | What you do |
|---|---|
| Pour water in until the level is just below the 60 mL mark. | |
| Add water a few drops at a time until the bottom of the meniscus sits on the 60 mL line. | |
| Stand the measuring cylinder on a flat, level bench. | |
| Check the reading one last time at eye level, then record it with its unit, mL. | |
| Bend down so your eye is level with the 60 mL line before you add any more water. |
Read the data: testing three thermometers
Scenario
A science club tests three thermometers by putting each one into the same beaker of water. A lab reference thermometer shows the water is really at 40.0 °C.
| Thermometer | Type | Range (°C) | Smallest step (°C) | Reading (°C) |
|---|---|---|---|---|
| A | Analog (liquid) | −10 to 110 | 1 | 40 |
| B | Digital probe | −40 to 200 | 0.1 | 43.6 |
| C | Digital | 0 to 50 | 0.1 | 40.1 |
Source: made-up test results for this worksheet.
1. Which thermometers are the most sensitive? Which one is the least accurate? Use numbers from Table 1.
2. Thermometer B always reads 3.6 °C too high. In a pot of water it shows 71.2 °C. What is the true temperature of the water? Show your working.
Answer °C
3. A café heats milk for coffee to about 65 °C. Which thermometer from Table 1 should it use? Explain why each of the other two is a worse choice.
4. Your school is setting up a weather station on the oval to record daily rainfall, as the Bureau of Meteorology does. You can use a rain gauge marked in 1 mm steps that holds up to 150 mm, or a straight-sided bucket marked in 50 mm steps that holds up to 500 mm. Which should you use? Justify your choice.
True or false
1. False: it measures the volume of a liquid, in millilitres. 2. False: neither type is always better; both can be accurate if good quality and read properly. 3. True. 4. False: that is range; sensitivity is the smallest change it can detect. 5. True. 5 correct = 3; 3 or 4 = 2; 1 or 2 = 1. [3 marks]
Choose the right instrument
Bean plant: ruler, cm (or mm). Water for a beaker: measuring cylinder, mL. Trolley: stopwatch, s. Tea: thermometer, °C. Marbles: balance, g. 1 mark per row, both cells correct. [5 marks]
Order the steps: measuring 60 mL of water
Reading down the table as printed, the correct step numbers are 2, 4, 1, 5, 3. In order: stand on a level bench; pour to just below 60 mL; eye level; add drops to the line; check and record. All correct = 2; three in the right place = 1. [2 marks]
Read the data: testing three thermometers
1. B and C, with 0.1 °C steps (1). B is least accurate: 43.6 °C is 3.6 °C above the true 40.0 °C (1). [2 marks]
2. 71.2 − 3.6 (1) = 67.6 °C (1). [2 marks]
3. Thermometer A: its range covers 65 °C, it read the true value (40 °C), and 1 °C steps are enough for milk (1). C is out of range: it stops at 50 °C (1). B covers the range but is not accurate: it reads 3.6 °C too high (1). [3 marks]
Question 4
Marking guide: 1 choose the rain gauge; 1 sensitivity: 1 mm steps record a light drizzle (e.g. 3 mm) that the bucket shows as nothing; 1 range: 150 mm covers almost every day; on a very wet day, read and empty it more often; 1 accuracy: state that finer marks alone do not prove accuracy and propose checking the gauge against a known volume or reference gauge for systematic error; 1 read at eye level, at the bottom of the meniscus; 1 conclusion: this lets rainfall be reported to the nearest millimetre. [6 marks]
Model answer: Use the rain gauge. It is more sensitive: its 1 mm steps record a 3 mm drizzle, which the bucket’s 50 mm steps would miss. Its 150 mm range covers almost every day; in a big storm we would read and empty it more often. The finer marks improve sensitivity, not necessarily accuracy. We would check accuracy against a known volume or calibrated reference gauge to detect systematic error. We read it at eye level, at the bottom of the meniscus, so we can report rainfall to the nearest millimetre.
Common error: choosing the bucket “because it has the bigger range”. Range only has to cover the values expected; here sensitivity decides.