infrared radiation

• All objects are continually absorbing and emitting infrared radiation
• Black bodies


  Perfect absorbers and emitters of radiation
• There are no known objects that are perfect at absorbing or emitting all the radiation, of every possible frequency, that may be directed at it
• Theoretical perfect black body

  • Absorbs all the radiation that falls on it
  • Does not reflect or transmit any radiation
  • Best possible emitter of 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
• Poor absorbers and emitters

  • White and shiny silvery surfaces
  • Reflect all visible light wavelengths
  • Do not emit radiation as quickly as darker colours
• Radiators in homes are usually painted white so that the infrared radiation is emitted gradually
• Black body


  Perfect absorber and emitter of radiation
• All objects are continually absorbing and emitting infrared radiation
• Investigating how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface


  1. Use appropriate apparatus to measure and record temperature accurately

  2. Make observations regarding the effects of electromagnetic waves on different substances
• Leslie cube


  • Metal cube with four different types of surface, filled with hot water to increase its temperature
• Procedure


  1. Place Leslie cube on heat-resistant mat

  2. Fill cube with boiling water and replace lid

  3. Leave for 1 minute to enable surfaces to heat up

  4. Use infrared detector to measure intensity of infrared radiation emitted from each surface, or temperature of surface

  5. Ensure detector is same distance from each surface for each reading
• The detector must be placed the same distance from each surface before taking a reading
• Control measures for boiling water hazard

  • Pour water slowly, using a funnel if necessary
  • Do not move the Leslie cube until it has cooled
• All objects are continually absorbing and emitting infrared radiation
• Black bodies


  Perfect absorbers and emitters of radiation
• Rate of absorption greater than rate of emission


  Temperature of the body increasing
• Rate of absorption equal to rate of emission

  Temperature of the body constant
• Rate of absorption less than rate of emission

  Temperature of the body decreasing
• Factors affecting the Earth's temperature


  • Concentration of greenhouse gases such as water vapour, methane and carbon dioxide
  • Rates at which light radiation and infrared radiation are absorbed and emitted by the Earth's surface and atmosphere
• How the Earth's temperature is affected

  1. Visible light and high frequency infrared radiation are absorbed by the Earth's surface, increasing its internal energy

  2. Some of this energy is transferred to the atmosphere by conduction and convection

  3. The Earth also radiates lower frequency infrared radiation

  4. Some of this infrared radiation is transmitted through the atmosphere back out into space

  5. Some is absorbed by greenhouse gases in the atmosphere, which then emit infrared radiation in all directions
• Greenhouse effect


  • Naturally occurring greenhouse gases, such as water vapour, stabilise the surface temperature of Earth and allow the planet to support life
  • Human activities are releasing additional carbon dioxide, causing more infrared radiation to be 'trapped' and reabsorbed by the Earth's surface, leading to global temperature increase and climate change