Black body radiation

• All objects are continually absorbing and emitting infrared radiation.
• Black bodies are perfect absorbers and emitters of radiation.
• A perfect black body is a theoretical object that absorbs all the radiation that falls on it and does not reflect or transmit any radiation.
• Stars are considered to be black bodies because they are very good emitters of most wavelengths in the electromagnetic spectrum.
• Planets and black holes are also treated as nearly perfect black bodies.
• White and shiny silvery surfaces are the worst absorbers, as they reflect all visible light wavelengths.
• Poor absorbers are also poor emitters, and do not emit radiation as quickly as darker colours.
• Radiators in homes are usually painted white so that the infrared radiation is emitted gradually.
• All objects are continually absorbing and emitting infrared radiation.
• Black bodies are perfect absorbers and emitters of radiation.
• The method described here uses a Leslie cube, a metal cube with four different types of surface, filled with hot water to increase its temperature.
• The aim of the experiment is to investigate how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface.
• The experiment involves placing a Leslie cube on a heat-resistant mat, filling it, almost to the top, with boiling water and replacing the lid, leaving for one minute to enable the surfaces to heat up to the temperature of the water.
• The infrared detector is used to measure the intensity of infrared radiation emitted from each surface, or the temperature of the surface.
• The detector must be placed the same distance from each surface before taking a reading.
• Hazards and control measures include boiling water, which can cause scalds, so pour water slowly, using a funnel if necessary, and do not move the Leslie cube until it has cooled.
• Black bodies are perfect absorbers and emitters of radiation.
• The temperature of a body is linked to the balance between the amount of radiation absorbed and emitted.
• The Earth's temperature depends on many factors including the concentration of greenhouse gases such as water vapour, methane and carbon dioxide.
• When visible light and high frequency infrared radiation are absorbed by the surface of the Earth, the planet’s internal energy increases and the surface gets hotter.
• Some of the energy transferred to the atmosphere by conduction and convection is then re-radiated back to Earth, which is then reabsorbed.
• The 'greenhouse effect' caused by naturally occurring greenhouse gases, such as water vapour, stabilises the surface temperature of Earth.
• Human activities such as deforestation and the burning of fossil fuels are releasing additional carbon dioxide, causing more infrared radiation to be 'trapped' and reabsorbed by the Earth’s surface.
• The enhanced greenhouse effect caused by these additional carbon dioxide emissions is causing global temperatures to increase, leading to climate change.