2.3.6Thermal Physics
Investigating IR Radiation — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
5 min read 10 parts Lesson 45 of 45 1 quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
2.3.6 Investigating IR Radiation — IGCSE PHYSICS notes: Plan and interpret experiments comparing the emission and absorption of infrared radiation by different surfaces.Aim — investigate how the infrared radiation absorbed or radiated by a surface depends on the nature of the sur…
- Independent variable
- Control variables
- Leslie cube
- All objects emit
- Conduction and convection
- Thermometer hole
Section 1 of 10Aim and variables
Aim
- Aim investigate how the infrared radiation absorbed or radiated by a surface depends on the nature of the surface
Independent variable
- Independent variable surface colour and texture
Dependent variable
- Dependent variable temperature
Control variables
- Control variables identical flasks except for colour, same amount of hot water, same starting temperature, same time interval, same room temperature
Section 2 of 10Equipment
| Equipment | Purpose |
|---|---|
| Heatproof mat | Protect the bench |
| Stopwatch | Time the cooling |
| Kettle | Boil water |
| Four thermometers | Measure the water temperature in each flask |
| Flasks painted black, dull grey, white and silver | Compare cooling of different surfaces |
Section 3 of 10Method for emission
1
Set up four identical flasks painted black, dull grey, white and silver.
2
Fill each with the same volume of hot water at the same starting temperature.
3
Record the starting temperature.
4
Record the temperature of each flask at regular intervals, for example every 30 s for 10 minutes.
5
The flask whose temperature falls fastest has the best-emitting surface.
Section 4 of 10Method for absorption
1
Take two identical metal plates, one matt black and one shiny silver.
2
Place them the same distance from a radiant heater with a thermometer or blob of wax on the back of each.
3
Switch on the heater and start the stopwatch.
4
The black plate shows the bigger temperature rise, or its wax melts first.
- Leslie cube
- alternative for emission, a hollow cube with faces of different finishes filled with hot water
- An infrared detector at equal distances gives the highest reading for matt black
- Shiny silver gives the lowest reading
Section 5 of 10Analysis
Analysis
All objects emit
- All objects emit hotter objects emit more infrared
Emission depends on
- Temperature of the body
- Surface area of the body
- Colour of the surface
Conduction and convection
- Conduction and convection cause most of the loss but are equal for each flask, so any difference is due to radiation
Graph
- Graph plot temperature on the y-axis against time on the x-axis and draw curves of best fit
- A steeper initial gradient means a better emitter
Findings
- Findings dull black is the best emitter and absorber, shiny silver the poorest emitter and absorber and the best reflector
Section 6 of 10Errors and improvements
Thermometer hole
- Thermometer hole keep it small, otherwise energy escapes through it
Parallax
- Parallax read the thermometer at eye level
Data logger
- Data logger gives more accurate readings with a digital thermometer
Random errors
- Random errors take repeat readings and avoid timing errors from starting the stopwatch in pairs
Lids
- Lids reduce loss by evaporation and convection so the main difference is radiation
Shielding
- Shielding protect a detector from other sources such as the Sun
Section 7 of 10Safety
Goggles
- Goggles wear them when filling flasks with boiling water
Electrics
- Electrics keep water away from electrical equipment
Burns
- Burns run any burn under cold water for at least 5 minutes
Kettle
- Kettle do not overfill it
Positioning
- Positioning keep equipment in the middle of the desk and stand to react to spills
Section 8 of 10More from the specification
1Radiant absorption by matte dark solids
- Radiant absorption by matte dark solids non-reflective black painted solids absorb incident thermal infrared radiation far more rapidly than polished metallic solids.
2Infrared Radiation and Surface Emission
- Thermal energy is transferred through infrared radiation without requiring a physical medium;
- matte black surfaces are superior emitters and absorbers of radiant heat compared to shiny, silvered tiles.
3Thermal Convection in Liquids and Gases
- When a liquid or gas is heated, warmer fluid expands, becomes less dense,
- and rises while cooler fluid sinks, setting up convection currents that drive bulk heat transfer.
4Terrestrial Energy Balance and Greenhouse Effect
- Solar radiation warms Earth's surface,
- which re-radiates thermal infrared wavelengths into space;
- greenhouse gases in the atmosphere absorb and re-emit this energy, trapping heat.
5Thermal equilibrium
- Constant temperature because energy is absorbed and lost at equal rates
6Potassium permanganate
- A purple compound used to show convection currents in water.
7Liquid
- State with a fixed volume that takes the shape of its container.
8Lattice
- The regular arrangement of atoms in a solid.
9Solid
- State with a fixed shape and a fixed volume.
10Vibration
- A repeated backwards and forwards movement.
11Energy transfer
- Movement of energy from one store to another.
12Energy transferred
- W = V Q, in joules.What the symbols mean: E or W = energy transferred (J) · Q = charge (C) · V = potential difference (V) · I = current (A) · t = time (s)
13Greenhouse effect
- Warming of the Earth because gases absorb and re-emit its infrared radiation
14Lattice vibrations
- Vibrations of atoms or ions about fixed positions that pass energy on
Section 9 of 10Key terms
| Term | Meaning |
|---|---|
| Emitter | Surface that gives out infrared radiation |
| Absorber | Surface that takes in infrared radiation |
| Independent variable | The variable deliberately changed |
| Dependent variable | The variable that is measured |
| Leslie cube | Hollow cube with faces of different finishes used to compare emission |
Section 10 of 10Exam technique
1
Mixing up emission and absorption experiments — an emission experiment measures cooling, an absorption experiment measures heating.
2
Saying a larger surface area changes the total energy to lose — it increases only the rate of emission.
3
Not controlling the starting temperature and volume of water — the test is then unfair.
4
Assuming conduction and convection differ between flasks — they are equal, so any difference is due to radiation.
Marked practiceQuizzes for this lesson
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