Light: "The Nature of Light" 1948 Coronet Instructional Films 10min
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Published on Aug 20, 2012
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"DEMONSTRATES LIGHT AS A FORM OF RADIANT ENERGY. EXPLAINS THE PRINCIPLES OF REFLECTION & REFRACTION & SHOWS HOW THESE PRINCIPLES APPLY TO THE SCIENCE OF OPTICS. SHOWS HOW 2 BOYS ON EARLY A.M. FISHING TRIP DISCOVER PRINCIPLES OF REFLECTION AND REFRACTION OF LIGHT THROUGH SIMPLE EXPERIMENTATION. DIAGRAMS EXPLAIN THE OPERATION OF CAMERA & HUMAN EYE."
Public domain film from the Library of Congress Prelinger Archive, slightly cropped to remove uneven edges, with the aspect ratio corrected, and 1-pass exposure & color correction applied (cannot be ideal in all scenes).
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
Visible light (commonly referred to simply as light) is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has a wavelength in the range of about 380 nanometres to about 740 nm -- between the invisible infrared, with longer wavelengths and the invisible ultraviolet, with shorter wavelengths.
Primary properties of visible light are intensity, propagation direction, frequency or wavelength spectrum, and polarisation, while its speed in a vacuum, 299,792,458 meters per second (about 300,000 kilometers per second), is one of the fundamental constants of nature. Visible light, as with all types of electromagnetic radiation (EMR) is experimentally found to move at exactly this same speed in vacuum.
In common with all types of EMR, visible light is emitted and absorbed in tiny "packets" called photons, and exhibits properties of both waves and particles. This property is referred to as the wave--particle duality. The study of light, known as optics, is an important research area in modern physics.
In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. This article focuses on visible light. See the electromagnetic radiation article for the general term...
Main article: Optics
The study of light and the interaction of light and matter is termed optics. The observation and study of optical phenomena such as rainbows and the aurora borealis offer many clues as to the nature of light.
Refraction is the bending of light rays when passing through a surface between one transparent material and another. It is described by Snell's Law: n_1\sin\theta_1 = n_2\sin\theta_2\ .
where \theta_1 is the angle between the ray and the surface normal in the first medium, \theta_2 is the angle between the ray and the surface normal in the second medium, and n1 and n2 are the indices of refraction, n = 1 in a vacuum and n is greater than 1 in a transparent substance.
When a beam of light crosses the boundary between a vacuum and another medium, or between two different media, the wavelength of the light changes, but the frequency remains constant. If the beam of light is not orthogonal (or rather normal) to the boundary, the change in wavelength results in a change in the direction of the beam. This change of direction is known as refraction.
The refractive quality of lenses is frequently used to manipulate light in order to change the apparent size of images. Magnifying glasses, spectacles, contact lenses, microscopes and refracting telescopes are all examples of this manipulation...
In the 1660s, Robert Hooke published a wave theory of light. Christiaan Huygens worked out his own wave theory of light in 1678, and published it in his Treatise on light in 1690. He proposed that light was emitted in all directions as a series of waves in a medium called the Luminiferous ether. As waves are not affected by gravity, it was assumed that they slowed down upon entering a denser medium...
The weakness of the wave theory was that light waves, like sound waves, would need a medium for transmission. A hypothetical substance called the luminiferous aether was proposed, but its existence was cast into strong doubt in the late nineteenth century by the Michelson-Morley experiment...
In 1900 Max Planck, attempting to explain black body radiation suggested that although light was a wave, these waves could gain or lose energy only in finite amounts related to their frequency. Planck called these "lumps" of light energy "quanta" (from a Latin word for "how much." In 1905, Albert Einstein used the idea of light quanta to explain the photoelectric effect, and suggested that these light quanta had a "real" existence. In 1923 Arthur Holly Compton showed that the wavelength shift seen when low intensity X-rays scattered from electrons (so called Compton scattering) could be explained by a particle-theory of X-rays, but not a wave theory. In 1926 Gilbert N. Lewis named these liqht quanta particles photons...
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