Infrared radiation and black bodies: Waves: Physics: GCSE (9:1)

• Infrared radiation


  Radiation that all bodies (objects) emit and absorb, no matter what temperature they are

  
• Good absorbers and emitters of infrared radiation

  Black and dull surfaces are the best absorbers and emitters, as they absorb all visible light wavelengths

  
• Poor absorbers and emitters of infrared radiation

  White and shiny silvery surfaces are the worst absorbers and emitters, as they reflect all visible light wavelengths

  
• Effect of temperature on infrared radiation emissions

  The hotter a body, the more infrared radiation it radiates in a given time and the greater proportion is emitted as visible light
• Black body


  A theoretical object that absorbs all of the radiation incident on it
• Properties of a black body

  It would absorb all the radiation that falls on it, would not reflect or transmit any radiation and would be the best possible emitter of radiation
• Why stars are considered to be black bodies

  They emit and absorb most wavelengths in the electromagnetic spectrum
• Other examples of black bodies

  Planets, black holes
• (higher-tier only)

  Rate of absorption and emission of infrared radiation


  Determines whether the temperature of a body is increasing, decreasing or constant
• (higher-tier only)

  When an object's temperature is increasing


  The rate of absorption of infrared is greater than the rate of emission
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  When an object's temperature is decreasing


  The rate of absorption of infrared is less than the rate of emission
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  When an object's temperature is constant


  The rate of absorption of infrared is equal to the rate of emission
• (higher-tier only)

  Factors affecting the Earth's temperature

  The rates of absorption and emission of radiation, reflection of radiation into space, concentration of greenhouse gases in the atmosphere

  
• (higher-tier only)

  The greenhouse effect

  Caused by naturally occurring greenhouse gases and stabilises the surface temperature of Earth