Blackbody Spectrucm and Planck’s Law
- Explain the concept of Blackbody Spectrum.
- Download PhET’s tool Blackbody Spectrum and associated activity titled Exploring Planck’s Law.
- Discuss the questions provided with the activity.
All objects with a temperature above absolute zero (0 K, -273.15 oC) emit energy in the form of electromagnetic radiation. A blackbody is a theoretical or model body which absorbs all radiation falling on it, reflecting or transmitting none. It is a hypothetical object which is a “perfect” absorber and a “perfect” emitter of radiation over all wavelengths. The spectral distribution of the thermal energy radiated by a blackbody (i.e. the pattern of the intensity of the radiation over a range of wavelengths or frequencies) depends only on its temperature.
Blackbody Radiation
The characteristics of blackbody radiation can be described in terms of several laws:
- Planck’s Law of blackbody radiation, a formula to determine the spectral energy density of the emission at each wavelength (Eλ) at a particular absolute temperature (T).
Planck's Law
- Wien’s Displacement Law, which states that the frequency of the peak of the emission (fmax) increases linearly with absolute temperature (T). Conversely, as the temperature of the body increases, the wavelength at the emission peak decreases.
Wien’s Displacement Law
- Stefan–Boltzmann Law, which relates the total energy emitted (E) to the absolute temperature (T).
Stefan-Botlzman's Law
Solve following activity to understand how Planck’s Law can be used to plot blackbody curves of objects with different temperatures, and the relationship between temperature and peak wavelengths in the electromagnetic spectrum. As the temperature decreases, the peak of the black-body radiation curve moves to lower intensities and longer wavelengths.
Verify yours answers by cheking with the answer key.