What is a Black Body? (Stefan Boltzmann's Law, emissivity, grey and white bodies...) - Physics
Physics Made Easy
A black body absorbs all light that is incident to its surface, but more importantly, when it has temperature, it emits light under the form of black body radiation.
In this video, we discuss the process in which a black body absorbs light, gains energy, and thus can re-emit it (under the form of… light). A great example being the Earth receiving light from the sun and remitting infra-red radiation.
We also discuss how a black body emits light when it has temperature, and why. This will bring us to Stefan Boltzmann’s Law that associate a luminosity (or power) to a temperature.
Real object are not black bodies but their behaviour can be more or less close. This idea is related to the concept of emissivity. This will let us introduce the ideas of grey and white bodies.
The black body model is used in many areas of Physics, like for example astrophysics, thermal physics and materials sciences. So it is essential to have an understanding of it to enjoy the multiple wonders that lie within these areas of physics.
The black body description in this video is based on classical physics theories.
Content of this video: 0:00 What is a black body? 0:30 The nature of light (Classical description) 1:21 Interaction of light with a black body 2:48 Emission of light by a black body 3:55 Stefan Boltzmann’s Law 4:35 Grey Bodies 4:50 What is emissivity? 5:31 Examples of grey and white bodies in the real world
Credit: Background that starts at 7 minutes and 33 seconds: Traverse galaxy Background: by F. Summers, G. Bacon (STScI). Simulation by C Hummels, P. Hopkins (CalTech) and A. Wetzel (UC Davis)
All other illustrations that are not credited in the video itself are by Edouard Reny or from the public domain.
Music by Edouard Reny.
This video is produced and presented by Edouard Reny, Ph.D. in solid state chemistry and private tutor in Physical Sciences.
For access to great resources that will help you with your studies of high school Physics (IB Physics, A Level Physics etc.), visit the "Physics Made Easy" website: https://www.physics-made-easy.com/
Edouard provides one-on-one private tuition in Physics (face to face or by Skype). If you wish to contact him, visit his website: https://www.physics-tutor.nl/
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