• Black body radiation is the name given to the?thermal radiation?emitted by all bodies (objects)
• All objects, no matter what temperature, emit black body radiation in the form of electromagnetic waves
• These electromagnetic waves usually lie in the?infrared?region of the spectrum but could be emitted in the form of visible light or other wavelengths, depending on the temperature
• The?hotter?object, the?more?infrared radiation it radiates in a given time

The infrared emitted from a hot object can be detected using a special camera

• A perfect black body is defined as:

An object that absorbs all of the radiation incident on it and does not reflect or transmit any radiation

• Since a good absorber is also a good emitter, a perfect black body would be the best possible emitter too
• As a result, an object which perfectly absorbs all radiation will be black
  • This is because the colour black is what is seen when?all?colours from the visible light spectrum are absorbed

   

Absorption and Emission For Different Colours Table

• All bodies (objects) emit a spectrum of thermal radiation in the form of electromagnetic waves
• The?intensity?and?wavelength?distribution of any emitted waves depends on the?temperature?of the body
• This is represented on a black body radiation curve
  • As the temperature increases, the peak of the curve moves

   

Black body spectrum for objects of different temperatures

• From the electromagnetic spectrum, waves with a?smaller?wavelength have?higher?energy (e.g. UV rays, X-rays)
• When an object gets hotter, the amount of?thermal radiation?it emits increases
  • This increases the thermal energy emitted and therefore the?wavelength?of the emitted radiation?decreases
• An ideal black body radiator is one that?absorbs and emits all wavelengths
  • This idealised black body is a theoretical object
  • However,?stars?are the best approximation there is
• The radiation emitted from a black body has a?characteristic spectrum?that is determined by the temperature alone

The intensity-wavelength graph shows how thermodynamic temperature links to the peak wavelength for four different bodies