6.4 Black Body Radiation

• What is black body radiation?

  Thermal radiation emitted by all bodies
• What type of waves does black body radiation emit?

  Electromagnetic waves
• In which region of the spectrum do most black body radiation waves lie?

  Infrared region
• How does the temperature of an object affect its black body radiation?

  Hotter objects emit more infrared radiation
• What can detect infrared radiation from hot objects?

  A special camera
• What defines a perfect black body?

  Absorbs all incident radiation without reflection
• Why is a perfect black body considered the best emitter?

  It absorbs all radiation, thus emits best
• Why does the color black appear when all colors are absorbed?

  All colors from visible light spectrum are absorbed
• How does temperature affect the emission of thermal radiation?

  • All bodies emit thermal radiation
  • Intensity and wavelength depend on temperature
  • Higher temperature shifts peak to lower wavelength
  • Higher temperature increases intensity of radiation
• What happens to the wavelength of emitted radiation as temperature increases?

  The wavelength decreases
• At what temperature does an object emit significant red light?

  At around 1000 °C

  
• What color light does an object emit at 6000 °C?

  Mainly white or blue light
• What type of radiation do objects emit at even higher temperatures?

  Ultraviolet or X-rays
• What occurs when an object absorbs thermal radiation?

  • The object becomes hotter
  • It emits more thermal radiation
  • Temperature increases if absorption exceeds emission
  • Equilibrium is reached when absorption equals emission
• What happens when an object absorbs radiation faster than it emits?

  The object heats up
• What is the result of an object reaching equilibrium in temperature?

  Constant temperature is maintained
• How can the temperature of a body be regulated?

  By balancing absorbed and emitted radiation
• How do emergency blankets keep trauma victims warm?

  By emitting less body heat through it
• What would happen to Earth's temperature without an atmosphere?

  It would drop to about −180 °C
• How does the Earth receive heat?

  Through thermal radiation from the Sun
• What happens to the thermal radiation emitted by the Earth?

  It has a longer wavelength than received radiation
• What role do greenhouse gases play in Earth's temperature?

  They absorb and reflect longer-wavelength radiation

  
• What is the greenhouse effect?

  A natural process that warms Earth's surface
• What happens to solar radiation when it reaches Earth's atmosphere?

  • Some radiation is reflected back to space
  • Non-reflected radiation is absorbed by greenhouse gases
  • Absorbed radiation warms the atmosphere and Earth's surface

  
• What should students be familiar with for exam questions regarding thermal radiation?

  Drawing and interpreting diagrams