Waves: Black Body Radiation

Waves: Black Body Radiation

Black Body Radiation

  • All objects emit and absorb electromagnetic radiation. The object’s temperature determines how much and the type of radiation it emits.
  • An object that absorbs all radiation falling on it and emits all possible frequencies is known as a black body.
  • As an object heats up, more radiation is given out across all frequencies and the peak frequency increases.
  • The sun is a good approximation of a black body, even though it is not a perfect black body. Its radiation has a peak in the visible light range of the spectrum.

Changes in Temperature

  • As the temperature of a black body increases, it emits more radiation in shorter wavelength frequencies.
  • When an object is heated, it first emits radiation in the infrared region, then as it gets hotter, in the visible light region, and then into the ultraviolet region as it gets even hotter.

Wien’s Displacement Law

  • According to Wien’s displacement law, the wavelength of the peak radiation is inversely proportional to the temperature of the body. It can be represented by the formula λ_max * T = b, where λ_max is the peak wavelength, T is the temperature, and b is a constant.

Stefan-Boltzmann Law

  • The total energy radiated per unit surface area of a black body is directly proportional to the fourth power of the black body’s temperature, represented by the Stefan-Boltzmann Law: P = σT⁴, where P is power, σ is the Stefan-Boltzmann constant, and T is temperature.

Uses and Applications

  • Understanding black body radiation has helped in the development of various technologies such as thermal imaging devices used by emergency services and in climate models used by scientists to predict global warming.
  • Infrared cameras can detect heat loss from a building by measuring the infrared radiation coming from the building, which is an aspect of black body radiation.

Black Body Radiation in Space

  • Cosmic Microwave Background Radiation (CMBR) is the afterglow of the Big Bang and is black body radiation.
  • The temperature of CMBR is about -270 °C and has a peak intensity in the microwave range of the electromagnetic spectrum.