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# The speed of light in water

### The light

Light is part of the electromagnetic radiation. Where it extends over a certain frequency range of this radiation and a person can see it. Unlike most other electromagnetic waves which are not visible to the human eye.

Color vision depends primarily on the nature of visible light and also depends on the analysis of these colors by the human eye and brain. While the human eye can see wavelengths ranging from 700 nanometers (red) to 400 nanometers (purple). Objects have no colors. Rather, seeing their colors depends on how light is reflected from their surface.

### The speed of light

Light travels at a speed of 1.07 billion kilometers per hour, or about 299,792,458 meters per second; Where light is the fastest of all things in the universe, so if a person moved at the same speed as light, he would be able to rotate around the Earth seven and a half times per second, for example, The average speed of Air travel is 800 kilometers per hour, which means that it takes 50 hours to go around the Earth. The Earth is a revolution, and this speed is constant in a vacuum and is indicated by the symbol C.

The light must travel from planet Earth to the moon by about one second, as the distance between them is estimated to be around 384,398.24 km and it takes about 8 minutes to travel from the sun to planet Earth, where the distance between them is estimated to be around 149,597,886 km, and for that; The value of the speed of light is used to measure astronomical distances. For example, the star closest to the Centaur (English: Proxima Centaur) is 4.25 light-years from Earth, which means that if the transition from planet Earth to this star were at the same speed of light, it would take 4 years and three months to get there.

### The speed of light in water

The speed of light is not constant. Since its speed can decrease depending on the medium in which it moves, and if there is no medium (in a vacuum), the speed of light in this case is at its maximum. When light passes through a region containing matter, even dust, it is refracted. This is the result of a collision with particles of these materials, which in turn leads to a decrease in the speed of light.

The rate of decrease of the speed of light depends on the medium, and this speed is called the refractive index of the medium and its value is in most cases greater than 1; As it was discovered by Jean Foucault in 1850 AD, for example, the refractive index of air is 1.0003, which is very close to the refractive index in a vacuum equal to 1. The refractive index of water is 1, 33, therefore to calculate the speed of light In water or any medium we use the law (speed = constant speed / refractive index of the medium), therefore; The speed of light in water is:

The speed of light in water = 299.792.458 / 1.33 = 225.407.863.16 meters per second.

The difference in the speed of light in water and air causes sunlight to refract as it enters the sea surface, then it is absorbed and dispersed by solid particles in the water. Most of the visible spectrum of light is absorbed within the first ten meters of the sea surface and the light cannot reach a depth of 150 meters even if the water is free of impurities. The diffusion or absorption of light in water depends on its wavelengths. While long wavelengths – such as red (penetrating up to the limit of 15 meters), yellow (penetrating up to the limit of 30 meters), and orange (penetrating up to the limit of 50 meters) – meters) – they enter the sea at shallower depths at short wavelengths such as purple, blue and green, which can also be reached at depths below the sea.

### The nature of light

Scientists discovered two natures of light in the 19th century, the first being that light is a ray and the other being that light is a wave. Where the theory was able to explain most of the known properties of light, namely: reflection, scattering, and refraction, but in the early 19th century AD, the English physicist Thomas Young (English: Thomas Young) has experimented called the Young Slit Experiment (English: Double-Slit Experiment) It involved shining a light through a small hole to drop it on a thin card with two holes, and behind this card is a screen; Thomas noticed the formation of bands of two colors on this screen and through this experiment it was discovered that the light has a wave nature.

At the beginning of the 20th century, the two scientists Planck (English: Planck) and Albert Einstein (English: Albert Einstein) concluded that light is made up of energy beams called photons, also considering light. The two different natures of light can be explained, namely that light is waves and that they are particles.

### Light properties

Some properties of light express its interaction with substances and these properties include the following:

Reflection: When light falls on a smooth surface, such as a mirror, for example, it will bounce the light off that surface at the same angle as the light.

Diffusion: When light falls on a non-smooth surface, it will bounce light in all directions and this feature is very important. Because it allows a person to look at things from different angles, for example, when light falls on the surface of a paper and spreads out, the person reading the paper can do so without having to change the angle reading.

Refraction: Refraction occurs when light passes through two transparent media such as air and water, causing the speed of light to change, causing it to bend towards the vertical line of incidence angle or away from it. A given means. Light is a part of electromagnetic radiation. Where it extends over a certain range of frequencies of this radiation, and a person can see it. Unlike most other electromagnetic waves that are not visible to the human eye.

Electromagnetic radiation is a form of energy and prepares radio waves, microwaves , x-rays , solar rays, gamma rays, in addition to visible light, which is a small part of it, all electromagnetic radiation.

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