Online educational resource on achieving indoor environmental quality with radiant based HVAC systems
Not for profit educational resource on indoor environmental quality.
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Using the, "Radiation Pressure of Light" to explain electromagnetic waves as an energy source.
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Radiation is sometimes a difficult topic to explain because it falls under the category of invisible principles, but in reality radiation can be seen in the form of light and felt in the form of heat. Light and heat are forms of energy. The power of light (a form of radiant energy) can be demonstrated by converting it's form into a form of kinetic energy as shown below. The key message to understand is radiation can be seen and felt and doesn't need air as an interstitial medium to reveal itself....and unlike air which can simultaneously exists in the same space at different densities and causes convection aka "cool air falls / hot air rises", radiant travels in all directions ergo it's incorrect to say heat rises when clearly it can travel in any direction - always from hot to cold.

Figure 1. The radiation pressure of direct sunlight is about 5 x N/. The effect of even less radiation can be shown with an apparatus where disks are placed at the ends of bars that are connected to a bearing. If one side of each disk is black and the other side is a mirror, then the light striking the black side is completely absorbed, so all the momentum of the light is transferred to the disk, while the light incident on the mirror is almost all reflected. Therefore the momentum transferred to the mirror is about twice as great as that transferred to the disk facing the light with its black side. The difference in momentum causes the rotor to rotate. It is important to ensure low friction at the bearing for the apparatus to work. In order to eliminate the effects of thermal expansion and air friction, the apparatus must be under high vacuum.

Citation: Sándor Kabai, The Radiation Pressure of Light, Wolfram Demonstrations Project, October 3, 2008


Note: This page has interactive demonstrations activated with Wolfram CDF player - a free viewing software tool for CDF files. To take full advantage of the educational content below download the Wolfram CDF player.

Learn more about radiant, light and other forms of heat transfer:
Human thermal plume
Conduction animation
Radiant animation
Convection animation
Mean radiant temperature

Emissivity, absorptivity and reflectivity
Seasons Simulator (NAAP)
Blackbody Curves & UBV Filters (NAAP)
Sun's Rays Simulator (NAAP)
Blackbody Curves of Melting (NAAP)
Sun Motions Demonstrator (NAAP)
Azimuth/Altitude Demonstrator (NAAP)

Hydrogen Atom Simulator
Infrared: Beyond the Visible (NASA)

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