Year 7 Science · Unit 4 · Lesson 4
Master Worksheet
Learning Goals
Compare: analog and digital thermometers
Complete the table. Each row compares the two types of thermometer.
| Feature | Analog thermometer | Digital thermometer |
|---|---|---|
| How the reading is shown | ||
| What could make it hard to use on a bush camp | ||
| One advantage it has over the other type | ||
| Another instrument of the same type (not a thermometer) |
Find the error: Noah’s lab notes
Noah’s lab notes
(1) I measured the mass of the rock with a measuring cylinder and got 24 mL. (2) The lab thermometer has a range of 10 °C to 110 °C, so I used it to check the freezer at −18 °C. (3) I read the bottom of the meniscus while looking down at the cylinder from above. (4) My stopwatch app is digital, so it shows the time as a number on a screen. (5) My new scale reads to 0.01 g, so its readings must be accurate.
1. Four of Noah’s five sentences contain one error each. For each wrong sentence, give its number and rewrite it correctly.
Plan a measurement: how much water evaporates?
Scenario
An open dish of water sits on a sunny windowsill for one school day. You expect the change to be small, perhaps only a few grams. You have a measuring cylinder marked in 1 mL steps, a digital balance that reads to 0.01 g (range 0 to 500 g), kitchen scales that read to the nearest 1 g, and a stopwatch.
Complete each part of the plan. The number in brackets is the marks for that part.
Instrument, and why its sensitivity matters here (2)
Method (3)
Calculation (2)
Sample results: dish and water at 8:30 am = 186.42 g; at 3:00 pm = 183.57 g. Work out the mass of water that evaporated.
Answer g
Read the data: choosing a balance
Scenario
A lab technician checks three digital balances with a reference mass that is exactly 20.00 g.
| Balance | Range | Smallest step (g) | Reading for the 20.00 g mass (g) |
|---|---|---|---|
| P | 0 to 5 kg | 1 | 20 |
| Q | 0 to 200 g | 0.01 | 20.00 |
| R | 0 to 500 g | 0.1 | 21.4 |
Source: made-up test results for this worksheet.
2. Rank the balances from most to least sensitive. Then name the balance that is sensitive but not accurate, and give the evidence from Table 1.
3. Choose the best balance for each job and give the deciding reason. (a) A 2.5 kg bag of flour. (b) A small leaf of about 0.5 g, which must be measured to the nearest 0.01 g. (c) A 150 g apple, to the nearest gram.
4. Evaluate this claim: “A digital instrument is always better than an analog one, because it gives a number.” Use range, sensitivity and accuracy, and at least one example from this worksheet.
Compare: analog and digital thermometers
1 mark per row, both cells (analog / digital). Shown: liquid line on a marked scale / number on a screen. Bush camp: must be read carefully at eye level, glass can break / battery can go flat. Advantage: needs no battery / quick and easy to read. Other: ruler, clock with hands, measuring cylinder / digital kitchen scales, phone stopwatch. [4 marks]
Find the error: Noah’s lab notes
1. (1) Use a balance, in grams (24 g, not mL) (1). (2) −18 °C is below its range; use a thermometer whose range goes lower (1). (3) Read the meniscus with your eye level with it, not from above (parallax) (1). (4) is correct. (5) 0.01 g steps are sensitivity; accuracy is closeness to the true value, so it could still read too high (1). [4 marks]
Plan a measurement: how much water evaporates?
Instrument: the digital balance (1); a change of a few grams needs 0.01 g steps, while kitchen scales show only whole grams (1). Method: weigh the dish and water at the start and record it (1); leave it on the windowsill all day, adding nothing (1); weigh it again on the same balance at the end and subtract (1). Calculation: 186.42 − 183.57 (1) = 2.85 g (1). [7 marks]
Read the data: choosing a balance
2. Q (0.01 g), then R (0.1 g), then P (1 g) (1). R: 0.1 g steps, but it read 21.4 g for a 20.00 g mass, 1.4 g too high (1). [2 marks]
3. (a) P, the only range that reaches 2.5 kg (1). (b) Q, the only one with 0.01 g steps, and accurate (1). (c) P or Q: both ranges cover 150 g and both read the test mass correctly; not R, which reads 1.4 g too high (1). [3 marks]
Question 4
Marking guide: 1 position (disagree: neither type is always better); 1 range: a digital instrument can have too small a range (Balance Q cannot weigh 2.5 kg); 1 smaller steps are sensitivity, not accuracy; 1 a digital reading can be far from the true value (R shows 21.4 g for 20.00 g); 1 an analog instrument needs no battery and is accurate if read at eye level; 1 judgement: choose by range, sensitivity and accuracy for the job. [6 marks]
Model answer: I disagree. Balance R shows 0.1 g steps but read 21.4 g for 20.00 g: sensitive, not accurate. Balance Q is digital but its range is too small for a 2.5 kg bag. An analog thermometer needs no battery and is accurate if read at eye level. The best instrument is the one whose range, sensitivity and accuracy suit the job.
Common error: treating more decimal places as more accuracy.