15.4: Blackbody Radiation

Describe the electromagnetic radiation emitted by an object due to its temperature.

• 15.4.A.1 Matter will spontaneously convert some of its internal thermal energy into electromagnetic energy.

• 15.4.A.2 A blackbody is an idealized model of matter that absorbs all radiation that falls on the body. If the body is in equilibrium at a constant temperature, then it must in turn emit energy.

• 15.4.A.3 A blackbody will emit a continuous spectrum that only depends on the body’s temperature. The radiation emitted by a blackbody is often modeled by plotting intensity as a function of wavelength.

  • 15.4.A.3.i The distribution of the intensity of a blackbody’s spectrum as a function of temperature cannot be modelled using only classical physics concepts. A blackbody’s spectrum is described by Planck’s law which assumes the energy of light is quantized.

  • 15.4.A.3.ii The peak wavelength emitted by a blackbody decreases with increasing temperature as described by Wien’s law.

• 15.4.A.3.iii The rate at which energy is emitted by a blackbody is proportional to the surface area of the matter and the temperature of the matter raised to the fourth power as described by the Stefan-Boltzmann law

15.4.A.3.ii The peak wavelength emitted by a blackbody decreases with increasing temperature as described by Wien’s law.

15.4.A.3.iii The rate at which energy is emitted by a blackbody is proportional to the surface area of the matter and the temperature of the matter raised to the fourth power as described by the Stefan-Boltzmann law