When we talk about the refraction of light we cannot help but talk about colors, the dispersion of light, the prism and the rainbow.
COLORS AND RAINBOW: REFRACTION OF LIGHT
Colors; dispersion of light ; spectrum and notes on infrared and ultraviolet rays. We usually deal with non-colored, “white” light, such as solar light. This is because ordinary visible light is a superposition of waves of various colors that give our eyes the result of white. With appropriate instruments, such as a prism , it is however possible, and Newton was the first to show it, to break down white visible light and see the colors it is composed of separately. This is thanks to the phenomenon of refraction and its dependence on wavelength.
REFRACTION OF LIGHT, PRISM
A prism is nothing more than a piece of glass of a suitable shape, such as a “pyramid”. In this case the two media are one, the air, where light usually travels, and the other, the glass.
The white light entering the prism separates into its constituent colors due to the effect of refraction, the angle of which depends on the wavelength, and when it exits again into the air, this separation is further accentuated.
Each wavelength corresponds to a different color. In this way, with an appropriate detector, which in many cases can also be simply the eye, it is possible to see the set of colors (also known as spectrum) that make up white light. The figure schematically represents the typical effect of decomposition of white light carried out by a prism :
The figure shows the spectrum of light visible to the human eye of electromagnetic radiation: only a part of it is the part visible to the human eye.
REFRACTION OF LIGHT: SIMPLE EXPLANATION. THE RAINBOW PHENOMENON
Sometimes we can see the decomposition of white sunlight into its visible spectrum in a spectacular natural phenomenon , thanks to the rainbow .
After a storm, a multitude of water droplets remain suspended high in the air, which, in particular lighting conditions (when the storm occurs near sunset and sunrise, with the sun low on the horizon), act like many prisms and allow us to see the spectrum of visible colors in the sky: red, yellow, blue, indigo, violet.
After a storm, many water droplets remain very high in the air and when the sun is low on the horizon (sunset or sunrise) the rainbow phenomenon can occur .
REFRACTION AND REFLECTION OF LIGHT: EXPLANATION
Refraction and reflection of light in a drop of water : the ray of sunlight undergoes refraction as it passes through and enters the surface of the drop of water, thus separating into the colours of the spectrum, and these then strike, from the inside, the second surface at an angle greater than the critical angle.
Then they are completely reflected, and then they come out again in the air backwards, from the same side that the original ray entered.
In this way, the separation into the component colors of the sun’s ray is obtained and the (primary) rainbow is seen. For this to happen, the angle between the sun and our eye (passing through the drop of water) must be about 42°.
