Why is sky blue and grass green?
First off, our eyes can only detect a small portion of electromagnetic spectrum known as visible region (400-700 nm in wavelength). Our retina has no sensitivity for radio, x-rays and other radiations outside of visible region.
(Source of image: http://www.sun.org/encyclopedia/electromagnetic-spectrum)
Color by reflection
Color in a substance can be produced from various mechanisms, most common of which is the reflection. An object is red because it absorbs all the color except red which is reflected back and detected by retina in our eyes. Grass is green because it produces a pigment name Chlorophyll (used for photosynthesis). Chlorophyll is a stronger absorbed of red and blue light and reflects green color and hence the color of the grass.
Color by scattering
But reflection is not the only mechanism by which color is produced like color of sky can be explained by a scattering phenomenon knows as "Rayleigh Scattering". Rayleigh found that scattering power of particles in inversely related to wavelength. Now, blue light has the smallest wavelength in visible region and hence strongly scattered by particles in the sky leading to blue color of the sky. But during sunset we see red color? During sunset sky appears yellow, orange or red (depending on atmosphere around you) because most of the blue light is already scattered and long-range wavelength colors are what left for us to see.
(Source of the image: http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html)
Color by radiation and electronic transition
Color can also be produced by radiation when a body is hot or due to electrons transitions. We already discussed in this post that a hot object can produce electromagnetic radiations via motion of atoms. One more mechanism of color is related to electrons. Electrons in an atom occupy specified states determined by quantum mechanics. By some sort of mechanism (heat etc.), these electrons can be excited to higher states and after sometime electrons would fall back to their original states and in doing so, releases photons of various wavelength. This phenomenon is used in LEDs bulbs. I will write a detailed post on that sometime in future.
(Source of image: http://www.sun.org/encyclopedia/electromagnetic-spectrum)
Color by reflection
Color in a substance can be produced from various mechanisms, most common of which is the reflection. An object is red because it absorbs all the color except red which is reflected back and detected by retina in our eyes. Grass is green because it produces a pigment name Chlorophyll (used for photosynthesis). Chlorophyll is a stronger absorbed of red and blue light and reflects green color and hence the color of the grass.
Color by scattering
But reflection is not the only mechanism by which color is produced like color of sky can be explained by a scattering phenomenon knows as "Rayleigh Scattering". Rayleigh found that scattering power of particles in inversely related to wavelength. Now, blue light has the smallest wavelength in visible region and hence strongly scattered by particles in the sky leading to blue color of the sky. But during sunset we see red color? During sunset sky appears yellow, orange or red (depending on atmosphere around you) because most of the blue light is already scattered and long-range wavelength colors are what left for us to see.
(Source of the image: http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html)
Color by radiation and electronic transition
Color can also be produced by radiation when a body is hot or due to electrons transitions. We already discussed in this post that a hot object can produce electromagnetic radiations via motion of atoms. One more mechanism of color is related to electrons. Electrons in an atom occupy specified states determined by quantum mechanics. By some sort of mechanism (heat etc.), these electrons can be excited to higher states and after sometime electrons would fall back to their original states and in doing so, releases photons of various wavelength. This phenomenon is used in LEDs bulbs. I will write a detailed post on that sometime in future.
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