What is black-body radiation and who coined the term?
Black-body radiation is the thermal electromagnetic radiation emitted by a body that absorbs all incoming radiation and reflects none. The term was introduced by Gustav Kirchhoff in 1860.
Questions about Black-body radiation
Short answers, pulled from the story.
What colors does a black body emit as its temperature increases?
A black body begins to glow dim red at around 525 degrees Celsius, the Draper point, then shifts through orange, yellow, and eventually a dazzling bluish-white at higher temperatures. When it appears white, a substantial fraction of its energy is being emitted as ultraviolet radiation.
What was the ultraviolet catastrophe in black-body radiation physics?
The ultraviolet catastrophe was the prediction made by classical physics that a black body should emit infinite energy at high frequencies, because each oscillation mode holds equal energy and there are infinitely many modes. The problem was resolved in 1901 by Max Planck, who showed that quantizing the energy of oscillators matched the experimental data.
What is Wien's displacement law and how does it apply to human body heat?
Wien's displacement law states that the peak emission wavelength of a black body is inversely proportional to its temperature. Applied to the human body, it places peak emission in the infrared, which is why thermal imaging devices for human subjects are designed to be most sensitive in the 7-14 micrometer range.
How is black-body radiation used to estimate Earth's temperature?
The Stefan-Boltzmann law is used to balance absorbed solar radiation against infrared emission from Earth. Using an albedo of 0.3 and a solar constant of 1372 watts per square meter, the calculation yields an effective temperature of 255 K, representing what Earth's surface temperature would be without any atmosphere.
What is the cosmic microwave background and how does it relate to black-body radiation?
The cosmic microwave background is the most perfect black-body radiation spectrum ever observed in nature, with a temperature of about 2.7 K. It is a record of the moment in the early universe when matter and radiation decoupled, after which that radiation has traveled freely through space.