Black Body Radiation

• What is black body radiation?

  Thermal radiation emitted by all bodies (objects)
• Do all objects emit black body radiation regardless of temperature?

  Yes, all objects emit black body radiation in the form of electromagnetic waves
• In which region of the spectrum do most electromagnetic waves from black body radiation lie?

  Infrared region
• What happens to the type of radiation emitted as the temperature of an object increases?

  The emitted radiation can shift from infrared to visible light or other wavelengths
• How does the intensity of infrared radiation emitted relate to the temperature of an object?

  The hotter the object, the more infrared radiation it radiates in a given time
• What is a perfect black body defined as?

  An object that absorbs all radiation incident on it without reflecting or transmitting any
• Why would a perfect black body be the best possible emitter of radiation?

  Because a good absorber is also a good emitter
• What color is seen when all colors from the visible light spectrum are absorbed?

  Black
• How does temperature affect the emission of thermal radiation from bodies?

  • All bodies emit a spectrum of thermal radiation
  • Intensity and wavelength distribution depend on temperature
  • As temperature increases, peak of the emission curve moves to lower wavelength and higher intensity
• What happens to the wavelength of emitted radiation as an object gets hotter?

  The wavelength of the emitted radiation decreases
• At what temperature does an object emit a significant amount of red light?

  At around 1000 °C

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

  White or blue light
• What type of radiation do objects emit at even higher temperatures than 6000 °C?

  Ultraviolet or even X-rays
• What happens to an object's temperature when it absorbs thermal radiation?

  The object becomes hotter
• What is thermal equilibrium?

  When an object absorbs radiation at the same rate it emits radiation
• How can an object maintain a constant temperature?

  By absorbing heat at the same rate as it loses heat
• What happens if an object absorbs radiation at a higher rate than it radiates?

  The object will heat up again
• What is the effect of a light-colored, shiny surface on thermal radiation emission?

  It emits less radiation than a dark, matte surface

  
• How do emergency blankets help keep trauma victims warm?

  By emitting less of their body heat through it
• What practical experiment can demonstrate the concept of thermal equilibrium?

  • Use a beaker of water at 50 °C
  • Monitor temperature with a thermometer
  • Heat water with a Bunsen burner
  • Adjust flame distance to maintain constant temperature
• What would happen to the Earth's temperature without an atmosphere?

  The temperature would drop to about −180 °C at night
• How does the Earth receive heat from the Sun?

  In the form of thermal radiation

  
• What happens to the thermal radiation emitted by the Earth?

  It has a slightly longer wavelength than the radiation received from the Sun

  
• What role do greenhouse gases play in the Earth's temperature?

  They absorb and reflect back longer-wavelength infrared radiation

  
• How do greenhouse gases contribute to warming the Earth?

  By absorbing radiation and then emitting it back to the surface

  
• What factors affect the temperature of the Earth?

  • Rate of light and infrared radiation reflected back into space
  • Rate of absorption by the Earth's atmosphere or surface
  • Rate of emission from the Earth's surface and atmosphere into space
• What is the Greenhouse Effect?

  • Natural process that warms the Earth's surface
  • Sun's thermal radiation reaches the atmosphere
  • Some radiation is reflected back to space
  • Non-reflected radiation is absorbed and re-radiated by greenhouse gases

  
• What should students be familiar with regarding thermal radiation in exams?

  Drawing and interpreting diagrams of thermal radiation absorption, emission, and reflection