Launch practical
About 60 minutes
- Set up the bench with the 9 items of apparatus.
- Take the readings yourself, into the results table you draw first.
- Process your results and plot the graph.
- Answer exam questions on your own results, which you mark against the mark scheme.
Runs in your browser: a 3D bench with 2D close-ups of each instrument for exact readings. Nothing to install and no account.
What you measure, and how
One run takes 32 readings. You take every one yourself, the way you would in class.
- On the 3D bench (Fig. 1) you set out the apparatus and read each instrument where it stands.
- In the 2D close-up (Fig. 2) the same instrument is drawn large, from the same run, for an exact reading. It is also how the practical runs on a device that cannot show 3D.
- In your table you write what you read, to the instrument’s resolution, and the notebook checks it against the instrument.
How to read it. Each small division is 1 °C. Read the top of the red liquid with your eye level with it, to the nearest half degree (0.5 °C).
What it shows
A good emitter is a good absorber
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.
The graph to expect. The type of surface is a categoric variable, so the Leslie cube results go on a bar chart, not a line graph. The flasks’ temperature against time is a curve: it falls fastest at the start, when the water is hottest.
Key equation for the exam: A matt black surface emits infrared fastest; a shiny silver one slowest..
No equation to learn. Learn the order of surfaces and that a good emitter is a good absorber.
Apparatus
| Item | What it is for | Resolution |
|---|---|---|
| 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 | An infrared thermometer, or an infrared detector with a meter: measures the infrared from each face. | 0.1 °C or 0.01 mV |
| Ruler and clamp | Keep the detector 5 cm from each face. | 1 mm |
| Four thermometers | The water in the cube and in each flask. | 1 °C divisions, read to 0.5 °C |
| Three flasks with lids | Painted matt black, painted matt white, and wrapped in shiny aluminium foil. | — |
| 250 ml measuring cylinder | The same volume of water in each flask. | 2 ml |
| Stopwatch | Times the flasks’ cooling. | 0.01 s |
Method
In our own words, as the Lab runs it. Your school's method sheet may differ in detail.
Which version are you doing?
Boards set this practical differently. Your course setting picks one; you can change it before you start.
Why: AQA compares the faces of a Leslie cube with an infrared detector, then three flasks; Edexcel compares four wrapped beakers cooling. The physics and the exam questions follow your board.
Clean the faces of the cube
Wipe each face with a clean, dry cloth, especially the shiny one.
Why: Greasy fingerprints are a thin film that emits infrared much better than polished metal.
Stand the cube on the heatproof matSafety
Put the Leslie cube on the heatproof mat, near the middle of the bench, before any hot water goes in. Stand the three flasks on the mat too.
Why: The cube will be full of very hot water: it must not be moved once it is full, and the bench must be protected.
Boil the kettle
Fill the kettle with enough water for the cube and the three flasks and switch it on. It stays on the side of the bench, by the socket.
Why: The hotter the water, the bigger the differences between the surfaces, so they are easier to measure.
Fix the distance to the detector
Choose how you will keep the detector the same distance (5 cm) from every face.
Do: Clamp it 5 cm from the face, measured with a ruler.
Why: Distance is the control variable to name here: a detector closer to the face receives more of its infrared.
Plan the order of your readings
The water cools by about half a degree every minute. Choose the order you will measure the four faces in.
Do: One reading of each face, then repeat the whole round.
Why: Every face should be measured with the water at the same temperature, or the comparison is not fair.
Measure the water for the flasks
Each flask needs the same volume of hot water (200 ml). If you use a measuring cylinder, read the bottom of the meniscus at eye level. Choose how you will measure it.
Do: Measure 200 ml into each flask with a measuring cylinder.
Why: More water stores more energy, so it cools more slowly. Equal volumes make the surface the only difference.
Start the flasks at the same temperature
Pour the hot water into a large beaker, stir it, then fill the three flasks from it one straight after another, and start the stopwatch.
Why: Hotter water cools faster, so a flask that starts cooler cools more slowly whatever its surface.
Take the readings
Leslie cube: fill it with hot water, then point the infrared thermometer at each of the four faces from the same distance, three readings of each, and read the water temperature at the start and end. Flasks: fill each with the same volume of hot water and read the temperature of each flask every 2 minutes for 10 minutes.
Repeats: Take three readings of each face, turning the cube between them, and calculate a mean. Repeats show whether readings cluster closely, and a mean reduces the effect of random errors (distance, a reading caught too soon). They do not remove systematic errors (fingerprints, leaning in).
Make safe and clear upSafety
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.
While you take readings
Point the detector straight at the face
Line the detector up so it points straight at the middle of the face, at right angles to it.
Why: At an angle the detector catches less of the face’s infrared and more of the room’s.
Wait for the reading to settle
After pointing the detector at a face, wait until the display stops changing before you record the reading.
Why: The detector takes a few seconds to warm up to the face it is pointing at.
Keep your hands and face back from the cube
Read the display from the side, with your hands and face well away from the hot cube.
Why: You emit infrared too. A shiny face reflects it into the detector. And the cube is hot enough to burn.
Hazards and control measures
| Hazard | What could happen | Control measure |
|---|---|---|
| Very hot water from the kettle | Scalds | Pour the water only where the cube and flasks stand, and never carry hot water across the lab |
| Hot metal faces of the cube | Burns | Do not touch the faces: turn the cube by its base and let it cool before emptying it |
| Kettle mains lead near water | Electric shock | Use a kettle with an undamaged lead, on a dry side bench away from the sink |
| 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 bench |
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. Clamp the detector 5 cm from the face, checked with a ruler.
- Temperature of the surfaces. All four faces are on one cube of water; measure them in quick rounds.
- Angle of the detector. Point it straight at the middle of each face.
- Volume and starting temperature of the water (flasks). 200 ml in each flask, all filled from the same beaker.
Results from a specimen run
| Surface | Reading 1 in °C | Reading 2 in °C | Reading 3 in °C | Mean temperature in °C |
|---|---|---|---|---|
| Matt black | 91.4 | 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 |
| When | Temperature of the water in °C |
|---|---|
| Start | 92.5 |
| End | 88.5 |
| 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 |
Anomaly spotted: Matt black face, reading 2, retaken.
Processing the data
- Showing the results
- A bar chart
- Mean for matt black
- 90.00 °C
- The best emitter
- Matt black
- The poorest emitter
- Shiny silver
- Matt black compared with shiny silver
- 65.4 °C
- Matt white
- Closer to matt black: matt white is a good emitter
- How much the matt black flask cooled
- 18.0 °C
- Which flask cooled fastest?
- Matt black
- Shape of the graph
- At the start, when the water was hottest
| Quantity | Specimen run | Accepted |
|---|---|---|
| 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 |
Common mistakes and the fix
Mistakes to check in this practical, and what to do instead. In a write-up or an exam answer, the mark goes to naming the step and saying what it does to the readings.
Method: Leave them
Fingerprints on the shiny silver face make it a slightly better emitter, so its readings come out a little too high (a systematic error on that face).
The fix: Clean the faces of the cube. Greasy fingerprints are a thin film that emits infrared much better than polished metal.
Method: Leave it on the bench
No effect on your data, but the hot cube marks the bench and is easier to knock: flagged in the safety review.
The fix: Stand the cube on the heatproof mat. The cube will be full of very hot water: it must not be moved once it is full, and the bench must be protected.
Method: Hold it about 5 cm away, judged by eye
The distance changes by up to a centimetre or two each time. An infrared detector’s readings then scatter by about ±20 %, enough to swap matt black and matt white. An infrared thermometer is hardly affected while its spot stays on the face.
The fix: Fix the distance to the detector. Distance is the control variable to name here: a detector closer to the face receives more of its infrared.
Exam answer: Leaving out: 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
The fix: The variable AQA wants: the distance between each face and the detector.
Exam answer: Leaving out: All four surfaces are at the same temperature (heated by the same water)
The fix: Say what is the same for all four faces: their temperature.
Worked exam-style questions
Written for Study Hack in the style of exam questions, on the specimen run above. They are not taken from any exam board's papers. Try each one before you open the worked answer.
- Question 1Control variables · Applying knowledge[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.
Worked answer and how the marks are given
A full-mark answer
The distance between each face of the cube and the infrared detector.
Mark scheme
- 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 Do not accept “room temperature”, “temperature of the room”, “type / colour / color / kind of surface / face”.
Where marks are usually lost
- Missing: 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. The variable AQA wants: the distance between each face and the detector.
- Question 2Mean of repeat readings · Applying knowledge[2 marks]
Use Table 1 to calculate the mean reading for the matt black surface.
Do not use the anomalous result.
Mean reading = °C
Worked answer and how the marks are given
A full-mark answer
mean = (91.6 + 88.5) ÷ 2
mean = 90.05 °CMark scheme
- (91.6 + 88.5) ÷ 2 (method)
- 90.05 °C (allow 90.0)
- Allow answers from 90.00 to 90.10 °C (the marker's tolerance; correct rounding of the student's own working is also accepted).
- A correct answer with no working scores full marks.
Where marks are usually lost
- Answer 81.1 °C (no marks). You included the anomalous reading (63.3 °C), which drags the mean down. Use only the two that agree: (91.6 + 88.5) ÷ 2 = 90.05 °C.
- Answer 122 °C (no marks). You added all three readings but divided by 2. Leave the anomaly out completely: (91.6 + 88.5) ÷ 2 = 90.05 °C.
- Missing: (91.6 + 88.5) ÷ 2. Add the two readings that agree, then divide by 2.
- Question 3Planning the flask method · Knowledge[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.
Worked answer and how the marks are given
A full-mark 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.Mark scheme
Indicative content:
- 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
Levels of response Level Marks What the answer does 3 5–6 A coherent method that would give valid results: all the important steps are there, in a sensible order. 2 3–4 A method that might not give valid results: most of the important steps are there, but some are missing or out of order. 1 1–2 A method that would not give valid results: some relevant steps are given, but they are not linked into a workable method. In Study Hack a six-mark answer is not given an automatic level: you tick the points your answer makes, then choose the level that fits it.
- No relevant content: 0 marks.
Evaluate
| Source of error | Type | Effect | Improvement |
|---|---|---|---|
| The distance from the detector to each face, judged by eye | Random | Readings of the same face vary, much more for an infrared detector than for an infrared thermometer. | Clamp the detector and set it 5 cm from each face with a ruler. |
| The water cooling while the faces are measured | Systematic | Faces measured later read lower, so the order of measurement changes the comparison. | Measure the faces in quick rounds, and record the water temperature at the start and end of each round. |
| Readings taken before the display settled | Random | Readings are low by different amounts, so repeats of the same face disagree. | Wait until the display stops changing before recording each reading. |
| The student’s own infrared reflected by the shiny face | Systematic | The shiny silver face always reads a little high, so it looks a better emitter than it is. | Stand back from the cube and keep hands away from the shiny face while reading. |
| Fingerprints on the shiny face | Systematic | The shiny face emits a little more than clean metal, so its readings are too high. | Wipe the faces clean and handle the cube only by its base. |
| The detector pointing at an angle to the face | Systematic | The detector receives less of the face’s infrared, so the differences between surfaces look smaller. | Point the detector straight at the middle of each face. |
| Flasks started at different temperatures | Systematic | A flask that starts cooler cools more slowly, whatever its surface. | Fill all the flasks from the same stirred beaker of hot water and check the start temperatures agree. |
| Different volumes of water in the flasks | Random | A flask with less water cools faster, so the falls in temperature vary from flask to flask. | Measure the same volume into each flask with a measuring cylinder. |
Repeatable. When you take repeat readings of the same face with the same detector, they cluster closely.
Reproducible. Another group, with a different detector or a different cube, finds the same order of surfaces.
Other exam boards
How this practical lines up with other GCSE boards' required or core practicals. Codes only; check your own specification for the exact activity.
| Board | Practical | Match | What is different |
|---|---|---|---|
| AQA | Required practical 10 | This page | — |
| Edexcel | 5.19P | Similar, with differences | Uses at least four beakers or tubes in different colours or finishes; this lab uses a Leslie cube. |
Print it
- Blank write-up: the nine-step lab book with the correct table headings, ready to print for a real lesson.
- Specimen lab book: this page's run written up in full, with its exam answers ticked against the mark scheme.
- Printable method card: the practical on one index card. Practise with the cards in Study Hack.
- Practical workbook: a full simulated data set to process on paper, with exam questions and answers.
- Teacher and technician pack: apparatus lists, technician notes and marking points.