- Thermometric Properties
- Defining A Temperature Scale
- Laboratory Thermometer
- Clinical Thermometer
- Maximum Thermometer
- Minimum Thermometer
- Three States Of Matter
- Brownian Motion
- Pressure In Gases
- Internal Energy
- Thermal Energy
- Heat Capacity
- Specific Heat Capacity
- Change Of State
- Melting and Solidification
- Boiling and Condensation
- Differences Between Boiling and Evaporation
- Specific Latent Heat
- Thermal Equilibrium
- Radiation (You Are Here!)
Radiation is the transfer of thermal energy from one place to another by means of electromagnetic radiation, without the need of an intervening material medium.
All matter radiate thermal energy in all directions in amounts determined by their temperature, where the energy is carried by photons, such as the infrared, visible and X-ray portions of the electromagnetic spectrum. These photons warm up anything that absorbs them.
Radiation is the only process that does not need a medium to transfer the energy.
Factors affecting the rate of radiation:
Colour and texture of surface
Black, matt surfaces are good in both absorbng and emitting radiation.
Shiny or polished white surfaces are poor absorbers because they act better as reflectors, and hence, poor emitters.
The hotter the object, the more energy it radiates
The grater the area, the more energy it radiates.
Applications of radiation
The greenhouse effect provides a means to grow plants that need a warm environment in cold countries. Short infrared radiation from the sun passes easily though the glass panels of a greenhouse, and is absorbed by the plants and soil inside. The plants in turn also radiate energy, but with a much longer wavelength. This radiation is reflected by the glass panels. Thus the temperature inside the greenhouse increases until it reaches a thermal equilibrium suitable for plants to grow.
A layer of aluminium sheet is placed below the roof tiles to keep the air temperature inside the building steady. In the day, the aluminium sheet reflects the radiation and keeps the building cooler. In the night, it reduces emitting radiation from the inside and keeps the interior warm.