Thermal radiation is a form of electromagnetic radiation emitted by any object with a temperature above absolute zero (-273.15°C or 0° Kelvin). It’s a result of the movement of charged particles within the matter.
Explanation of Thermal Radiation
- All matter consists of atoms and molecules in constant motion. This motion has kinetic energy, which is associated with the temperature of an object. As temperature increases, the motion of the particles becomes more agitated. This causes charged particles within the matter (like protons and electrons) to accelerate and change their energy states.
Emission of Energy
- When charged particles change energy states, they release energy in the form of electromagnetic waves.
- The frequency and intensity of this radiation depend directly on the object’s temperature.
The Spectrum of Thermal Radiation
- Thermal radiation covers a wide range of the electromagnetic spectrum. However, much of it falls within the infrared region, which we experience as heat. Hotter objects emit more thermal radiation and a higher proportion of radiation in the visible light spectrum. This is why very hot objects can start to glow red or white.
Examples
- The Sun: A primary source of thermal radiation. Its high surface temperature causes it to emit a broad spectrum of electromagnetic radiation, including infrared, visible light, and ultraviolet radiation.
- A Radiator: Designed to emit heat through thermal radiation, warming a room.
- The Human Body: Emits infrared radiation, which is why thermal imaging cameras can detect us in the dark.
- The Earth: Absorbs solar radiation and then emits thermal radiation back out into space.
Key Points
- A Constant Process: As long as an object has some internal heat, it emits thermal radiation.
- Heat Transfer Thermal radiation is one of the three main forms of heat transfer (alongside conduction and convection).
- Universal Phenomenon: Thermal radiation occurs throughout the universe, from stars to everyday objects.
| Light sources | Emission mechanism | Description | Examples |
|---|---|---|---|
| LIGHT-EMITTING PROCESS | |||
| Luminescence | Light emission due to the excitation of electrons in a material. | Electrons within a material gain energy and then release light as they return to a lower energy state. | Bioelectroluminescence Electroluminescence Photoluminescence - Fluorescence - Phosphorescence Sonoluminescence Thermoluminescence |
| Blackbody radiation (Type of thermal radiation) | Electromagnetic radiation (including visible light) emitted by any object with a temperature above absolute zero. | Electromagnetic radiation (including visible light) emitted by any object with a temperature above absolute zero. | All objects above temperature of absolute zero. |
| Chemiluminescence | Light from natural and artificial chemical reactions. | Light from natural and artificial chemical reactions. | Bioluminescence Chemiluminescent reactions: - Luminol reactions - Ruthenium chemiluminescence |
| Nuclear reaction | Light emission as a byproduct of nuclear reactions (fusion or fission). | Light emitted as a byproduct of nuclear reactions. | Nuclear reactors Stars undergoing fusion |
| Thermal radiation | Light emission due to the thermal excitation of atoms and molecules at high temperatures. | Light emission due to the thermal excitation of atoms and molecules. | Sun Stars Incandescent light bulbs |
| Triboluminescence | Light emission due to mechanical stress applied to a material. | Light emission due to the mechanical stress applied to a material, causing the movement of electric charges and subsequent light emission. | Sugar crystals cracking Adhesive tape peeling Quartz crystals fracturing. |
| Natural light source | |||
| Fireflies Deep-sea creatures Glowing mushrooms | Bioluminescence | Light emission from biological organisms. | Involves the luciferase enzyme. |
| Sun Stars | Nuclear Fusion | Light emission as a byproduct of nuclear fusion reactions in stars. | Electromagnetic spectrum (visible light, infrared, ultraviolet). |
| Fire Candles | Thermal radiation | Light emission due to the thermal excitation of atoms and molecules during the combustion of a fuel source. | Burning of a fuel source, releasing heat and light. |
| Artificial light source | |||
| Fluorescent lights Highlighters Safety vests | Chemiluminescence | Light emission from chemical reactions. | Fluorescence (absorption and re-emission of light). |
| Glow sticks Emergency signs | Chemiluminescence | Light emission due to phosphorescence - a type of chemiluminescence. | A type of chemiluminescence where light emission is delayed after the initial excitation. |
| Glow sticks Light sticks | Chemiluminescence | Chemiluminescence | Light emission from a chemical reaction that does not involve combustion. |
| Tungsten light bulbs Toasters | Thermal radiation | Heated filament radiates light and heat. | Light emission from a hot filament. |
| Fluorescent lamps LED lights | Electroluminescence | Excitation of atoms by electric current. | Light emission when electric current excites atoms in a material. |
| Neon signs | Electrical Discharge | Discharge of electricity through gas. | Light emission when electricity flows through a gas. |
| Sugar crystals cracking Pressure-sensitive adhesives | Triboluminescence | Light emission from friction or pressure. | Light emission due to mechanical forces. |
| Fluorescent paint Highlighters Safety vests | Photoluminescence | Absorption and subsequent re-emission of light at a lower energy. | Absorption and re-emission of light. |
Light Sources: Mechanism, examples, and everyday applications
Footnote: Cerenkov radiation and Synchrotron radiation are not included in the table because they are not conventionally classified as light sources.