الضوء .. الفيزياء

Light .. Physics

Light

The human eye is sensitive to a narrow range of electromagnetic radiation, the wavelength of which is called light, ranges between 760 and 380. The eye's response to these waves varies according to the length of each nanometer, where it generates a feeling of a special color different from the rest of the colors.

It is worth noting that a beam of light is nothing but a group of individual rays that travel in a straight line and move almost in one direction. The greatest evidence of the straight spread of light is the eclipse and the accuracy of the shadows that light creates.

A body is not visible unless it is an emitter of light, such as the sun and an electric lamp, or a reflector of it, such as the moon. When a beam of light falls on an object, part of it is reflected on its surface, and another part sometimes penetrates into it, while the remaining part is absorbed by the object. The law of reflection of light states that the angle of incidence S equals the angle of reflection V, and that light is reflected on the surface of a smooth and well-polished body and takes a specific direction. However, if the surface of the body is rough and not smooth, the light is reflected on it and disperses in all directions. The speed of light in the air does not differ from its maximum speed, which in a vacuum is 300 thousand km per second. If a light beam traveling through the air enters another medium, such as glass or water, its speed decreases, and its wavelength decreases accordingly because its frequency does not change, and its direction changes, of course. When light passes between two media of different densities, it bends or refracts in a direction perpendicular to the space separating the two media. It is worth noting that the ratio of the speed of light in a vacuum (or in air to some extent) to its speed in a dense medium is a fixed ratio called the refractive index N, and it is equal to 1.5 in glass and about 1.34 in water. The law of refraction states that the refractive index N is equal to the ratio of the sine of the angle of incidence S to the sine of the angle of refraction K.
(Bottom) Solar eclipse as seen from different locations on the Earth's surface.
(Left) Reflection and refraction of light.