Why does a blue book appear black in red monochromatic light? I found the question on this website but it doesn't provide an explanation.
[Physics] Why does a blue book appear black in red monochromatic light
opticsvisible-light
Related Solutions
Human color vision is based on four types of receptors in the retina: rods, and three types of cones. Their response to different wavelengths is shown in this graph:
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It shows clearly how certain wavelenghts, mostly around the yellow-green portion of the spectrum, are absorbed more strongly, and by more types of cells, than the rest.
So it is normal that, even with equal powers, some colors are seen brighter than others. Actually, digital cameras often filter their CCD array with a Bayer mask, which has twice as many pixels filtered green, as red or blue, to better simulate the eye's color sensitivity.
Jon Custer hinted at something, which I think is best explained via an analogy.
Imagine you can walk along a pavement at 4mph. When the pavement is empty, it takes you an hour to travel four miles. But when the pavement is crowded, you're dodging around people and bumping into them. You're still walking at 4mph, but it takes you an hour and a half to travel the four miles. And if you're a little old lady with short little steps walking at 4mph, you're held up more than if you're a big guy with long strides walking at 4mph. Now let's look at your questions again:
But I wonder why their speeds differ in any other medium?
Because the light interacts with the material, and those interactions are wavelength dependent.
And why Red light travels faster while it has less energy than blue light?
Because the light interacts with the material, and those interactions are wavelength dependent!
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Best Answer
This occurs because the blue book absorbs all the red, leaving nothing to be reflected, so it appears black.
White light is made up of all the different colors (wavelengths) of visible light. Some of the colors are absorbed by an object and some are reflected. We view reflected light, and we do not view absorbed light. For example, say you're wearing a red t-shirt. The reason it appears red is it reflects more red light than anything else. Objects appear black when they absorb all colors, and objects appear white when they reflect all colors.
This website gives more information about the appearance of color due to reflection. Hope this helps!