Physics Classroom says:
It's no longer a drab, black and white world. The world is filled to the brim with color. Clothing, automobiles, televisions, computer monitors, and printed media are no longer the black and white creatures of yesteryear. We walk and move and touch and see in a world that oozes with color.
But how does it work? How do objects get colored? How do our eyes perceive color? What is the physics associated with the topic of color? These are the questions that we will explore in this gallery of The Physics Classroom Flickr site. We will use the photos of other Flickr photographers to take an elementary journey into our world of color.
Physics Classroom says:
We should begin our journey into the world of color where Isaac Newton began it many centuries ago. It was Newton who first explained the dispersion of white light into its component colors. This band of colors was called a spectrum; it is sometimes referred to as the ROYGBIV spectrum of visible light. Each letter in the acronym ROYGBIV stands for a separate color. For instance, R stands for red, O for orange, and so on.
For Newton, white light was composed of color - particles of color. The color was present in the white light. And since each color traveled at different speeds through the prism, the prism simply caused the colors to fan out and become distinguishable from one another. The observation of the rainbow of colors provided the evidence that white light consisted of a variety of component colors.
Today, scientists explain the dispersion using a wave theory. Light behaves as a wave and the various colors of white light are each associated with a wave of a different wavelength.
Physics Classroom says:
When a low pressure gas such as hydrogen is heated or somehow energized, it gives off light. When analyzed using a diffraction grating (or similar apparatus), the light that is emitted is observed to have certain discrete wavelengths. Rather than consisting of a continuous spectrum of wavelengths, the emitted light is characterized by only certain wavelengths - for example, a blue wavelength and a red wavelength. The photo at the right depicts a portion of the line spectrum of hydrogen gas.
Scientists have determined that these wavelengths of light (and their associated energy) is related to electrons in the atom changing from a high energy to a lower energy state. The difference in energy of the electron is equal to the energy of the emitted light.
Physics Classroom says:
The world we see is a world that is illuminated either by sunlight or by the light emitted by incandescent and fluorescent light bulbs. All three sources of light provide white light - ROYGBIV light. So we can think of this light as being filled with color. All objects that we view are more or less illuminated by the same light. So why do we view different objects to have different colors?
The answer has to do with pigments. Colored objects contain pigments or chemicals that are capable of selectively absorbing certain wavelengths of light that are present within the ROYGBIV spectrum. For instance, leaves contain chlorophyll which absorb mostly ROYBIV, leaving the G to be reflected. During the fall, leaves produce anthocyanins - pigments that absorb OYGBIV, leaving the R to be reflected.
Physics Classroom says:
The color possessed by clothing, paper, inks, paints, etc. are due to the presence of specific pigments within the objects. These pigments are found in nature as naturally occurring chemicals. Scientists have learned to isolate these chemicals, and in some instances to artificially manufacture them. When present in objects such as fabrics, paper, etc., the chemicals selectively absorb wavelengths of light within the ROYGBIV spectrum. The colors of light that are not absorbed are reflected to our eye.
The process of selectively absorbing light is sometimes referred to as color subtraction. In the most simplest terms, a physicist would picture the situation as follows: ROYGBIV approaches an object, one or more of the colors (wavelengths of light) is absorbed (i.e, subtracted), and the remaining colors are reflected to our eye. The process could be represented by a simple equation:
ROYGBIV - OYGBIV = R = red
To learn more about color subtraction, visit The Physics Classroom Tutorial.
Physics Classroom says:
There are two types of photoreceptors on the retina - rods and cones. There are approximately 120 million rods, each capable of detecting light intensity or brightness. There are approximately 6 million cones capable of detecting wavelengths of light within the visible light spectrum. The photograph at the right is a colorized version of a scanning electron micrograph (SEM) of rods and cones on the retinal surface. The rods are pictured in yellow and the cones in green.
There are three types of cones that are distinguished from one another based upon the wavelengths of light that they are most sensitive to. The cones are sometimes referred to as the "red cones", the "green cones" and the "blue cones". While the three cone types can detect more than one color, the name they are given is associated with the color of light that they are most sensitive to.
Physics Classroom says:
The photo at the right depicts the result of shining red, green and blue spotlights on a vase of flowers sitting upon a bench and projecting the shadows onto a white screen. This demonstration depicts principles of both color addition and color subtraction. The vase, stems and flowers block the light that shines upon them, thus creating the colored shadows we see in the photograph. Since there are three spotlights, there are three shadows - one shadow for each light that is blocked. For instance, the cyan shadow on the left is the result of blocking the light from the red spotlight; this is color subtraction. The blue light and green light are not blocked and thus reach the white screen and combine to produce the cyan shadow of the object; this is color addition. Similarly, the magenta shadow is the result of blocking the green light and allowing the red and blue light to combine to produce the magenta shadow.
Finally, observe that there are locations where two shadows overlap. At these locations, we view a primary color of light. For instance, the red part of the flower is the result of overlapping the yellow shadow (from which blue is absent) and the magenta shadow (from which green is absent). Once blue and green is subtracted, the only color remaining is red; thus, the overlap appears red.
A similar photo can be found in The Physics Classroom's photostream.
To learn more about color shadows, visit The Physics Classroom's Shockwave Physics Studios.
Physics Classroom says:
The Physics Classroom is always grateful to those Flickr photographers who have used their skills to capture the nature of the physical world. Because of their willingness to share their work, they have added both color and beauty to this gallery and many others.
We hope that you have enjoyed this gallery and the brief exploration of the physics of color. You are welcome to view our other completed galleries in the Galleries section of The Physics Classroom Flickr site.
And if you wish to learn more about the physics of your world, visit The Physics Classroom Website.
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