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Specimen lab book: Infrared radiation
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Study Hack Lab
RP 10 · Physics
Infrared radiation
Lab book
Name
Specimen
Date
2 November 2026
Course
GCSE Physics
Board and specification
AQA GCSE Physics (8463), 4.6.2.2AQA GCSE Combined Science: Trilogy (8464), 6.6.2.2Apparatus and techniques: AT 1, AT 4
Run
C29HO
Status
Finished: every stage done
Exam questions
30/30 marks
Aim
Investigate how the amount of infrared radiation a surface emits depends on the nature of the surface: with a Leslie cube, then with three flasks cooling.
Contents
Plan and risk assessment
Apparatus
Method
Results
Graph
Analysis
Conclusion and evaluation
Make safe and clear up
Exam questions on your data
Simulated data produced by Study Hack Lab from the student's own run (seed 20261004). Every reading, value and mark here is from that run; nothing has been retyped. Layout v1, practical v2. Original material; not affiliated with AQA, which has not reviewed it.
1 Plan and risk assessment
Every object emits infrared radiation, and hotter objects emit more. At the same temperature, a matt black surface emits the most and a shiny silver (polished metal) surface the least. Matt white paint is nearly as good an emitter as matt black: in the infrared it is the shininess that matters, not the colour.
A good emitter is a good absorber
Variables
Independent (you change)
Type of surface
Dependent (you measure)
Detector reading (amount of infrared emitted) in °C or mV
Control (you keep the same)
Distance between each face and the detector; Temperature of the surfaces; Angle of the detector; Volume and starting temperature of the water (flasks)
Prediction
All four faces of the cube are at the same temperature. Which face will emit the most infrared?
Matt blackRight first time
Dark, matt surfaces are the best emitters (and absorbers) of infrared.
Which face will emit the least infrared?
Shiny silverRight first time
Light, shiny surfaces are the poorest emitters (and absorbers) of infrared. Polished metal is the poorest of all.
How will the matt white face compare with the matt black face?
Almost as much infrared as matt black.Right first time
Your matt white mean was 86.0 °C, against 90.0 for matt black and 24.6 for shiny silver. White paint looks white because it reflects visible light, but in infrared it behaves like a dark surface: it emits almost as well as matt black. Class data often shows matt white and shiny black giving the same reading. It is shininess, not colour, that makes a poor emitter.
Risk assessment
Hazard
Harm it could cause
Control you chose
Very hot water from the kettle
Scalds
Pour the water only where the cube and flasks stand, and never carry hot water across the labRight first time
Hot metal faces of the cube
Burns
Do not touch the faces: turn the cube by its base and let it cool before emptying itRight first time
Kettle mains lead near water
Electric shock
Use a kettle with an undamaged lead, on a dry side bench away from the sinkRight first time
Hot water knocked over from the cube or a flask
Scalds to the legs and lap
Work standing up, with everything on the heatproof mat away from the edge of the benchRight first time
2 Apparatus
✓Leslie cube with lid Four faces at the same temperature: matt black, shiny black, matt white and shiny silver.
✓Kettle Very hot water for the cube and the flasks.
✓Heatproof mat Under the cube and the flasks.
✓Infrared detector (resolution 0.1 °C or 0.01 mV) An infrared thermometer, or an infrared detector with a meter: measures the infrared from each face.
✓Ruler and clamp (resolution 1 mm) Keep the detector 5 cm from each face.
✓Four thermometers (resolution 1 °C divisions, read to 0.5 °C) The water in the cube and in each flask.
✓Three flasks with lids Painted matt black, painted matt white, and wrapped in shiny aluminium foil.
✓250 ml measuring cylinder (resolution 2 ml) The same volume of water in each flask.
✓Stopwatch (resolution 0.01 s) Times the flasks’ cooling.
3 Method: your choices
Which version are you doing?: AQA required practical 10: a Leslie cube, then three flasksInfrared from four faces at the same temperature, then three flasks cooling for 10 minutes.
Clean the faces of the cube: DoneGreasy fingerprints are a thin film that emits infrared much better than polished metal.
Stand the cube on the heatproof matSafety: DoneThe cube will be full of very hot water: it must not be moved once it is full, and the bench must be protected.
Fix the distance to the detector: Clamp it 5 cm from the face, measured with a rulerThe distance is the same for every reading, to about 1–2 mm, so it is a fair test of the surfaces.
Plan the order of your readings: One reading of each face, then repeat the whole roundEach face is measured early, in the middle and late, so the cooling of the water affects every face equally.
Measure the water for the flasks: Measure 200 ml into each flask with a measuring cylinderEach flask holds 200 ml to within a couple of millilitres.
Start the flasks at the same temperature: DoneHotter water cools faster, so a flask that starts cooler cools more slowly whatever its surface.
Point the detector straight at the face: DoneAt an angle the detector catches less of the face’s infrared and more of the room’s.
Wait for the reading to settle: DoneThe detector takes a few seconds to warm up to the face it is pointing at.
Keep your hands and face back from the cube: DoneYou emit infrared too. A shiny face reflects it into the detector. And the cube is hot enough to burn.
4 Results
32 of 32 readings taken.
The Leslie cube · Infrared thermometer 5 cm from each face.
Surface
Reading 1 in °C
Reading 2 in °C
Reading 3 in °C
Mean temperature in °C
Matt black
91.4
59.1, crossed out,90.1
88.5
90.0
Shiny black
88.3
86.9
85.4
86.9
Matt white
87.5
86.0
84.6
86.0
Shiny silver
24.8
24.6
24.5
24.6
The water in the cube
When
Temperature of the water in °C
Start
92.5
End
88.5
The three flasks · 200 ml of hot water in each flask.
Time in minutes
Temperature of the matt black flask in °C
Matt white in °C
Shiny silver in °C
0
83.0
82.5
83.0
2
78.5
78.5
80.0
4
75.0
74.5
77.5
6
71.5
71.0
75.5
8
68.0
68.5
73.5
10
65.0
65.5
71.0
Fall in 10 minutes
18.0
17.0
12.0
0.0 Struck through: the anomaly, retaken; the new reading is beside it.
Anomaly: Matt black face, reading 2, retaken. Likely cause: the detector was not set up properly for that reading: knocked out of line with the middle of the face, pointing partly past the edge, or knocked further away than the others.
5 Graph
Cooling curve for the matt black flask
6 Analysis
Showing the results
You want to compare the mean readings for the four surfaces. Which type of chart should you draw?
A bar chartRight first time
Mean for matt black
mean = sum of the values ÷ number of values
Calculate the mean reading for the matt black face.
90.00 °CRight first time
The best emitter
Your means: Matt black 90.0 °C · Shiny black 86.9 °C · Matt white 86.0 °C · Shiny silver 24.6 °C. Which surface emitted the most infrared?
Matt blackRight first time
The poorest emitter
Your means: Matt black 90.0 °C · Shiny black 86.9 °C · Matt white 86.0 °C · Shiny silver 24.6 °C. Which surface emitted the least infrared?
Shiny silverRight first time
Matt black compared with shiny silver
difference = mean (matt black) − mean (shiny silver)
Calculate how much bigger the matt black mean is than the shiny silver mean.
65.4 °CRight first time
Matt white
Many students predict that white is a poor emitter. Your means: Matt black 90.0 °C · Shiny black 86.9 °C · Matt white 86.0 °C · Shiny silver 24.6 °C. Is matt white closer to matt black or to shiny silver?
Closer to matt black: matt white is a good emitterRight first time
How much the matt black flask cooled
fall in temperature = starting temperature − final temperature
Calculate the fall in temperature of the matt black flask over the 10 minutes.
18.0 °CRight first time
Which flask cooled fastest?
Falls in temperature over 10 minutes: Matt black 18.0 °C · Matt white 17.0 °C · Shiny silver 12.0 °C. Which flask cooled fastest? Readings are to 0.5 °C, so if two falls are within a degree of each other, either is a right answer.
Matt blackRight first time
Shape of the graph
When was the matt black flask cooling fastest?
At the start, when the water was hottestRight first time
7 Conclusion and evaluation
Quantity
Your value
Accepted value
Matt black − shiny silver (careful readings)
65.4 °C
64.7 °C
Fall of the matt black flask in 10 minutes
18.0 °C
17.4 °C
Conclusion
What do your results show about the surfaces?
Matt surfaces emit more infrared than shiny ones; shiny silver (polished metal) is by far the poorest emitter.Right first time
Your means: matt black 90.0, matt white 86.0, shiny silver 24.6 °C. All four faces are at the same temperature, so the difference is the surface. Matt white is nearly as good as matt black, so it is not colour alone: shiny metal is the poor emitter.
Sources of error
The distance from the detector to each face, judged by eye: systematic or random?
RandomRight first time
Readings of the same face vary, much more for an infrared detector than for an infrared thermometer.
The water cooling while the faces are measured: systematic or random?
SystematicRight first time
Faces measured later read lower, so the order of measurement changes the comparison.
Readings taken before the display settled: systematic or random?
RandomRight first time
Readings are low by different amounts, so repeats of the same face disagree.
The student’s own infrared reflected by the shiny face: systematic or random?
SystematicRight first time
The shiny silver face always reads a little high, so it looks a better emitter than it is.
Fingerprints on the shiny face: systematic or random?
SystematicRight first time
The shiny face emits a little more than clean metal, so its readings are too high.
The detector pointing at an angle to the face: systematic or random?
SystematicRight first time
The detector receives less of the face’s infrared, so the differences between surfaces look smaller.
Flasks started at different temperatures: systematic or random?
SystematicRight first time
A flask that starts cooler cools more slowly, whatever its surface.
Different volumes of water in the flasks: systematic or random?
RandomRight first time
A flask with less water cools faster, so the falls in temperature vary from flask to flask.
Improvement
Which change would most improve your results?
Measure the faces in quick rounds, and record the water temperature at the start and end of each round.Right first time
Repeatable or reproducible
Your three readings of the matt black face are close together. This shows your readings are…
RepeatableRight first time
Repeatable: the same person, method and equipment give similar results.
Another group uses a different Leslie cube and a different detector, and finds the same order of surfaces. This shows the result is…
ReproducibleRight first time
Reproducible: a different person, method or equipment gives similar results.
8 Make safe and clear up
Switch off and unplug the kettle; leave the cube and flasks to cool on the mat
When cool, empty the cube and the flasks into the sink with the lids off
Dry the cube and wipe the shiny face so it is ready for the next class
Switch off the detector and put the thermometers back in their case
9 Exam questions on your data
On your own readings, self-marked against the mark scheme, with error carried forward where it applies. Total 30/30.
01.1[1 mark]
A student used a Leslie cube filled with very hot water and an infrared detector to compare four different surfaces.
Give one variable the student should control.
Your answer
The distance between each side of the cube and the detector.
1/1 self-marked
Distance between each side (of the cube) and the (infrared) detector; allow temperature of the water (or of the surfaces); allow angle of the detector to the face
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: The distance between each face of the cube and the infrared detector.
01.2[2 marks]
The four surfaces are the four sides of one hollow metal cube, filled with the same hot water.
Explain why this makes the investigation a fair test.
Your answer
All four surfaces are at the same temperature, so the only thing that changes is the type of surface.
2/2 self-marked
All four surfaces are at the same temperature (heated by the same water)
So the only variable that changes is the type of surface (any difference in the readings is caused by the surface)
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: All four surfaces are at the same temperature because the same hot water heats them, so the only variable that changes is the type of surface.
01.3[1 mark]
Give one way to make the Leslie cube investigation safer.
Your answer
Do not touch the hot cube.
1/1 self-marked
One workable precaution: keep hands off the hot cube; stand while working (a spill cannot land in a lap); use water a little below boiling; stand the cube on a heatproof mat. Not creditworthy: using cold water; a vague "be careful" with no action
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: Do not touch the hot cube. (Or: stand while you work, or use water a little below boiling.)
01.4[1 mark]
You used an infrared thermometer. A liquid-in-glass thermometer with its bulb painted matt black can also be used as the detector.
Give one advantage of using an infrared thermometer rather than the blackened-bulb thermometer.
Your answer
It has a higher resolution and gives a reading more quickly.
1/1 self-marked
Higher resolution (0.1 °C rather than 1 °C); or responds more quickly / reading settles faster; allow easier to read (digital display); allow more precise
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: The infrared thermometer has a higher resolution (0.1 °C rather than 1 °C). (Or: it responds more quickly.)
02.1[1 mark]
Another student did the same investigation with the same kit. For one reading the detector was not lined up properly with the face.
Table 1 shows the student’s readings.
Which reading is anomalous?
Select one row.
Table 1
Surface
Reading number
Reading in °C
Matt black
1
91.6
Matt black
2
63.3
Matt black
3
88.5
Shiny black
1
88.0
Shiny black
2
87.0
Shiny black
3
85.8
Matt white
1
87.3
Matt white
2
86.2
Matt white
3
84.9
Shiny silver
1
25.1
Shiny silver
2
24.9
Shiny silver
3
24.8
Your answer
matt black reading 2
1/1
Matt black reading 2: far from the other two readings for that surface, which agree
Full marks. Well done. Matt black reading 2 (63.3 °C) is far from the other two readings of the same surface (91.6 and 88.5 °C).
Model answer: Matt black, reading 2. It is much lower than the other two readings for that surface, which agree with each other.
02.2[2 marks]
Use Table 1 to calculate the mean reading for the matt black surface.
Do not use the anomalous result.
Your answer
90.05
Working: mean = (91.6 + 88.5) ÷ 2
mean = 90.05 °C
2/2
(91.6 + 88.5) ÷ 2
90.05 °C (allow 90.0)
Full marks. Clear and precise.
Model answer: mean = (91.6 + 88.5) ÷ 2
mean = 90.05 °C
02.3[1 mark]
The results should be shown on a bar chart, not a line graph.
Give the reason why.
Your answer
The type of surface is a categoric variable, not a continuous one.
1/1 self-marked
The type of surface (the independent variable) is a categoric variable; allow not continuous; allow the surfaces are words, not numbers
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: The type of surface is a categoric variable.
02.4[2 marks]
Your mean readings were: matt black 90.0 °C, matt white 86.0 °C, shiny silver 24.6 °C.
Before the practical, a student predicted: “The matt white surface will emit much less infrared than the matt black surface, because white is a poor emitter.”
Use your results to explain whether the student’s prediction was correct.
Your answer
The prediction was not correct. Matt white gave 86.0 °C, almost as much as matt black at 90.0 °C.
2/2 self-marked
The prediction was not correct: matt white emits almost as much infrared as matt black (it is a good emitter)
Uses the data: matt white 86.0 °C is close to matt black 90.0 °C (and far above shiny silver 24.6 °C); allow the difference quoted
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: The prediction was not correct. Matt white (86.0 °C) emitted almost as much infrared as matt black (90.0 °C), and far more than shiny silver (24.6 °C). Matt white is a good emitter of infrared.
02.5[1 mark]
Another student measured each surface once. Table 2 shows the results.
Table 2
Surface
Reading in °C
Matt black
69
Shiny black
67
Matt white
67
Shiny silver
23
What is wrong with the way the student collected these data?
Your answer
The measurements have not been repeated to show that they cluster closely.
1/1 self-marked
Each surface was measured only once: there are no repeat readings to show the readings agree. Not credited here: repeats justified only by accuracy, an average or anomalies
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: Each surface was measured only once. The readings should have been repeated to show whether they agree closely.
02.6[2 marks]
The student in Table 2 concluded:
“Black surfaces emit more infrared than white surfaces.”
Evaluate the student’s conclusion. Use data from Table 2.
Your answer
The conclusion is not always true: matt white and shiny black both read 67 °C, so a white surface emitted the same as a black surface.
2/2 self-marked
The data do not support “black always emits more than white” (only part of it holds). Just saying the conclusion is wrong is not enough
The readings for the matt white and shiny black surfaces are both 67 °C; or a (matt) white surface emits the same as a (shiny) black surface
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: The conclusion only partly holds. Matt black did give the highest reading, but the matt white and shiny black surfaces both gave 67 °C, so the data do not show that every black surface emits more than every white one.
03.1[6 marks]
A student has two flasks. One is painted matt black. The other is covered in shiny aluminium foil.
The student also has a kettle, two thermometers, a measuring cylinder and a stopwatch.
The student’s hypothesis is: “Hot water in a matt black flask transfers energy to the surroundings faster than hot water in a shiny flask.”
Describe a method the student could use to test the hypothesis.
Your answer
Heat water in a kettle.
Use a measuring cylinder to pour the same volume of hot water (200 cm³) into each flask.
Put a lid and a thermometer into each flask.
Record the initial temperature of the water in both flasks and start a stopwatch.
Record the temperatures again after 10 minutes.
Calculate the change in temperature (the decrease) for each flask.
Compare the results: if the matt black flask has the larger decrease, the hypothesis is supported.
Keep the starting temperature, the volume and the flasks’ size the same, and repeat the experiment.
6/6 self-marked
Heat the water (in a kettle)
The same measured volume of hot water in each flask (measuring cylinder)
Insert a thermometer into each flask
Record the initial temperature of the water in both flasks
Record the temperatures after a set time (e.g. after 10 minutes, or every minute)
Calculate the change (decrease) in temperature for each flask
Compare the results to test the hypothesis (bigger decrease = faster energy transfer)
Same starting temperature / same size flasks / lids on / repeat
Self-marked: Level 3, 6 of 6 marks. You ticked 8 of 8 indicative points. This is your own judgement against the mark scheme.
Model answer: Heat water in a kettle.
Use a measuring cylinder to pour the same volume of hot water (200 cm³) into each flask.
Put a lid and a thermometer into each flask.
Record the initial temperature of the water in both flasks and start a stopwatch.
Record the temperatures again after 10 minutes.
Calculate the change in temperature (the decrease) for each flask.
Compare the results: if the matt black flask has the larger decrease, the hypothesis is supported.
Keep the starting temperature, the volume and the flasks’ size the same, and repeat the experiment.
03.2[1 mark]
A student fills identical flasks with hot water. Each flask has a different type of surface. She measures how quickly the temperature of the water in each flask falls.
Give one variable, other than the type of surface, that should be kept the same for the flasks.
Your answer
The volume of water in each flask.
1/1 self-marked
Volume (or mass) of water; or starting temperature of the water; or size / type of flask; or lid; or time the temperatures are taken; allow room temperature
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: The volume of water in each flask. (Or: the starting temperature of the water.)
03.3[2 marks]
Table 3 shows your temperature readings for the matt black flask.
Table 3
Time in minutes
Temperature in °C
0
83.0
2
78.5
4
75.0
6
71.5
8
68.0
10
65.0
Calculate the mean rate of decrease in temperature of the water over the 10 minutes.
Your answer
1.8
Working: decrease = 83.0 − 65.0 = 18 °C
rate = 18 ÷ 10 = 1.8 °C per minute
2/2
Decrease in temperature = 83.0 − 65.0 = 18 °C
1.8 °C per minute
Full marks. That is exactly what the mark scheme is looking for.
Model answer: decrease = 83.0 − 65.0 = 18 °C
rate = 18 ÷ 10 = 1.8 °C per minute
03.4[2 marks]
Look again at Table 3.
When was the rate of decrease in temperature greatest?
Give a reason for your answer. Use data from Table 3.
Your answer
During the first 2 minutes, when it fell by 4.5 °C, because the temperature difference between the water and the surroundings was greatest.
2/2 self-marked
During the first 2 minutes; allow at the start
A reason from the data: the fall of 4.5 °C was bigger than in any later 2 minutes; or the water was hottest, so the temperature difference with the surroundings was greatest
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: During the first 2 minutes: the temperature fell by 4.5 °C, more than in any later 2 minutes. The water was hottest then, so the temperature difference between the water and the surroundings was greatest.
03.5[2 marks]
In 10 minutes the temperature of the water in your flasks fell by:
matt black 18 °C, matt white 17 °C, shiny silver (foil) 12 °C.
Explain what these results show about shiny surfaces.
Your answer
The shiny flask cooled the least, by 12 °C, because shiny surfaces are poor emitters of infrared radiation.
2/2 self-marked
The shiny (foil) flask cooled the least / most slowly (fall of 12 °C)
Because shiny surfaces are poor emitters of infrared (emit less infrared)
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: The shiny flask cooled the least (its temperature fell by only 12 °C), because shiny surfaces are poor emitters of infrared, so energy is transferred from the water more slowly.
04.1[2 marks]
Another student tests how well surfaces absorb infrared.
Two metal plates stand at equal distances from a radiant heater. One plate is matt black and one is shiny silver. A coin is stuck to the back of each plate with candle wax.
Explain which coin will fall off first.
Your answer
The coin on the matt black plate, because matt black is a better absorber of infrared so it heats up faster and the wax melts first.
2/2 self-marked
The coin on the matt black plate
Matt black is a better absorber of infrared, so its temperature increases faster (the wax melts first)
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: The coin on the matt black plate falls first, because matt black is a better absorber of infrared, so its temperature increases faster and the wax melts first.
04.2[1 mark]
A surface is a good emitter of infrared radiation.
Which statement about the surface is correct?
Tick (✓) one box.
It is a good reflector of infrared.
✓ It is a good absorber of infrared. (your choice)
It must be black.
It is shiny.
Your answer
It is a good absorber of infrared.
1/1
It is a good absorber of infrared.
Full marks. Your answer meets all the points for this question.
Model answer: It is a good absorber of infrared.
Unseen data: the same skills, new apparatus
01[3 marks]
A student fills two identical drinks cans with the same volume of hot water. One can is painted matt black; the other is shiny. They read the temperature of each every 2 minutes.
Temperature of the water
Time in min
Matt black can in °C
Shiny can in °C
0
73.7
73.7
2
69.7
71.3
4
66.2
69.3
6
62.8
67.2
8
59.7
65.3
10
57.0
63.4
Calculate the mean rate of cooling of the matt black can between 2 minutes and 8 minutes, in °C per minute. Give your answer to 2 significant figures.
Your answer
1.7
Working: 69.7 - 59.7 = 10.0
8 - 2 = 6
10.0 / 6
3/3
Fall = 69.7 − 59.7 = 10.0 °C.
Time taken = 8 − 2 = 6 min.
Mean rate = fall ÷ time taken, in °C per minute.
Full marks. That is exactly what the mark scheme is looking for.
Model answer: Fall = 69.7 − 59.7 = 10.0 °C in 8 − 2 = 6 minutes.
Mean rate of cooling = 10.0 ÷ 6 = 1.7 °C per minute.
02[2 marks]
A student paints four identical test tubes, fills each with the same volume of cold water, and stands them the same distance from a radiant heater for 5 minutes.
Rise in temperature in 5 minutes
Surface
Rise in °C
Matt black
9.5
Shiny black
7.4
Matt white
5.0
Shiny silver
2.7
Which TWO conclusions do these results support? Tick (✓) two boxes.
✓ Of the two black tubes, the matt one absorbed more infrared than the shiny one. (your choice)
✓ The matt black tube absorbed more infrared than the matt white tube. (your choice)
The results prove that every black surface absorbs more infrared than every white surface.
The shiny silver tube absorbed the most infrared, but reflected it away.
All four tubes absorbed the same amount of infrared, because they were the same distance from the heater.
Your answer
Of the two black tubes, the matt one absorbed more infrared than the shiny one.; The matt black tube absorbed more infrared than the matt white tube.
2/2
Of the two black tubes, the matt one absorbed more infrared than the shiny one.
The matt black tube absorbed more infrared than the matt white tube.
Full marks. That is exactly what the mark scheme is looking for.
Model answer: Matt black rose 9.5 °C against shiny black 7.4 °C (matt absorbs more than shiny), and against matt white 5.0 °C (black absorbs more than white). One test of four tubes supports these conclusions; it cannot prove them for every surface.
03[2 marks]
Another student fills a Leslie cube with hot water. They hold an infrared detector by hand in front of each face in turn, taking three readings of one face before moving on to the next.
Which TWO changes would make the comparison of the four faces more valid? Tick (✓) two boxes.
✓ Clamp the detector so that it is the same distance from every face. (your choice)
✓ Read each face once in turn, then repeat the round, so the water has cooled by about the same amount for every face. (your choice)
Use cold water, so the cube is safe to touch.
Take five readings of each face instead of three, so that each reading is accurate.
Paint the detector matt black so it absorbs more infrared.
Your answer
Clamp the detector so that it is the same distance from every face.; Read each face once in turn, then repeat the round, so the water has cooled by about the same amount for every face.
2/2
Clamp the detector so that it is the same distance from every face.
Read each face once in turn, then repeat the round, so the water has cooled by about the same amount for every face.
Full marks. That is exactly what the mark scheme is looking for.
Model answer: The distance from each face to the detector is a control variable: clamp it. Reading the faces in rounds spreads the water’s cooling evenly over the four faces, so the last face is not measured when the water is cooler. Cold water would give readings too small to tell the faces apart.