--- title: "Infrared Emission, Absorption and the Temperature of a Body" description: "Ordinary objects above absolute zero emit thermal radiation. Emission depends on temperature and surface properties. Controlled comparisons of matt black paint and polished metal show how surfaces aff" canonical: https://lightmysky.com/learn/science/infrared-emission-absorption-and-the-temperature-of-a-body-mt_xwh9uZ8gCl source: https://lightmysky.com/learn/science/infrared-emission-absorption-and-the-temperature-of-a-body-mt_xwh9uZ8gCl.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Infrared Emission, Absorption and the Temperature of a Body Ordinary objects above absolute zero emit thermal radiation. Emission depends on temperature and surface properties. Controlled comparisons of matt black paint and polished metal show how surfaces affect radiative heating and cooling. Earth's average temperature also depends on absorbed sunlight and thermal radiation escaping to space. Subject: Science · Area: Waves, Light & Sound · Ages 15 to 16 Page: https://lightmysky.com/learn/science/infrared-emission-absorption-and-the-temperature-of-a-body-mt_xwh9uZ8gCl ## Ready when they can - Predicts how matt black paint and polished metal affect radiative heating and cooling in a controlled comparison - Uses total energy input and output rates to explain temperature changes for an object with fixed heat capacity and no change of state - Explains how increased atmospheric infrared absorption can disturb Earth's energy balance and change average surface temperature ## Lesson: Infrared and a body's temperature You have met infrared in the electromagnetic spectrum. Ordinary objects above absolute zero emit thermal radiation, mostly infrared at everyday temperatures. Radiation needs no material medium, so sunlight can cross space and warm skin. Conduction needs matter in contact; convection carries energy in moving fluids. Matt black paint usually absorbs and emits infrared well. Polished metal usually reflects infrared and emits little at the same temperature. Good absorption and good emission are linked at the same wavelength. Visible colour alone does not tell you infrared behaviour: white paint can emit infrared well too. **Example.** Compare identical cans with equal heat capacities and initial temperatures above the same cooler, uniform surroundings. Match exposed areas and radiation exposure. With other transfers matched, matt black paint usually gives greater net radiative loss than polished metal. Without phase changes or changes in other energy stores, this means faster cooling. In sunlight, ordinary black paint absorbs more, but warming also depends on heat capacity and losses. *(drawing: Radiation is the only transfer here. Both rates are 8 W, so the object's energy stays constant while emission continues.)* Only thermal energy stores change in this model. Mass and heat capacity stay fixed, and no phase change occurs. Net power is total input minus total output. Positive net power warms the object; negative net power cools it. Zero net power keeps its temperature steady while transfers continue. With equal heat capacities, larger positive net power gives faster warming. Count every transfer, including conduction, convection, radiation and internal heating. Start with the Earth-atmosphere system in energy balance: absorbed sunlight equals radiation escaping to space. The surface emits infrared. Greenhouse gases absorb some infrared and emit upward and downward. Suppose increased absorption reduces the initial escape of energy while absorbed sunlight stays fixed. The system then gains energy and warms until outgoing radiation again matches absorbed sunlight. For fixed surface area and unchanged emissivity, total emitted thermal power is proportional to T^4. Emissivity measures how effectively a surface emits compared with an ideal emitter. T is temperature in kelvin. Total emission includes all wavelengths, not just infrared. Net radiative loss also accounts for radiation absorbed from the surroundings. **Recap.** Surface properties affect radiation. With fixed heat capacity, no phase change and no changes in other energy stores, balanced total input and output keep temperature steady. *This lesson, its questions and flashcards were written for this dataset. Scientific source records were used for facts and teaching design; their wording is not reproduced.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [The Electromagnetic Spectrum: Uses and Dangers](https://lightmysky.com/learn/science/the-electromagnetic-spectrum-uses-and-dangers-mt_P_NXNSo1zQ) - [Conduction, convection, and radiation](https://lightmysky.com/learn/science/conduction-convection-and-radiation-mt_ySnOkVIu22) ## Optional connections - [Specific heat capacity as a material property](https://lightmysky.com/learn/science/specific-heat-capacity-as-a-material-property-mt_mXC9IKom3P) ## Opens up - [Blackbody Radiation and the Quantum of Energy](https://lightmysky.com/learn/science/blackbody-radiation-and-the-quantum-of-energy-mt_B2Bk2IAOa9) - [Earth's Energy Balance and the Greenhouse Effect, Quantified](https://lightmysky.com/learn/science/earths-energy-balance-and-the-greenhouse-effect-quantified-mt_dDV2fr06nO)