Light travels constant @ speed, so it does not slow down? But what happens when it shines into a deep ocean?

Question

Does it change form? & if so what is the transformation called? Sunlight vs flashlight vs laser beam how would each differ if shined into very deep ocean?

Answer 1

Light is an electromagnetic wave, and as such the propagation of light depends upon the electrical properties of the medium. Macroscopically, the interaction is described by the complex refractive index of the medium. The refractive index can in principle be calculated from the quantum mechanics of the atoms and molecules that comprise the medium. In the case of the ocean, most of the refractive index comes from water, but the ions in solution will also make a contribution. Light will undergo scattering, absorption and refraction. Scattering occurs where there is a change in refractive index. There is a complex wavelength dependence, but as a rule of thumb scattering is strongest when the wavelength of the light is comparable to the length scale of the scattering centre. Because the ocean is fairly homogeneous, scattering is weak. The same light incident on your flesh is scattered at every cell boundary and looses all directionality within 3 mm. Absorption is determined by the imaginary part of the refractive index and is wavelength dependent. Visible wavelengths with penetrate tens of meters with little attenuation whereas 99.9% of infrared radiation at 3 microns will be absorbed within 10 microns. The source of the light does not matter if the wavelength is the same. Refraction is governed by the real part of the refractive index and is a measure of the speed of light in the medium. The refractive index is wavelength dependent, so if a short pulse of light with 2 wavelengths was sent into the ocean, a detector would receive the signal from one wavelength before the other. Sunlight and a flashlight are essentially polychromatic thermal sources, so all of the wavelenght dependent effects mentioned above would be apparent. Lasers are quasi monochromatic light sources, so the wavelenght dependence is not important.

Answer 2

Light travels at a constant speed, period. But it travels at different (slower) constant speeds for different media. The fastest constant speed is the speed of light in a vacuum. Other constant speeds are slower, but how much slower depends on the material the light is traveling through.

Light is made up of packets of energy...E = hf; where h = Plank's constant and f = frequency of the energy packets. When these packets hit something, they can be absorbed or reflected (diffused). Thus, rushing at the speed of light suitable for the medium they are in (e.g., ocean water), they smash into water molecules and are either diffused or absorbed (depending on energy levels and the angles of attack).

Coherent light is light made up of energy packets of the same frequency and, therefore energy. Coherent light, such as found in lasers, is less likely to diffuse than ordinary light, such as found coming from a flashlight. It's for this reason, coherent light can be used to measure extreme distances such as from Earth to the Moon (and back), while ordinary light cannot be used because it would disperse before it could reach the Moon.

Sunlight and flashlight are made up of particles (photons) at a variety of energy levels (frequencies); so light from these sources will be attenuated via absorptions or diffusion faster than comparable laser light. This is one reason the Navy uses a blue-green chemical laser to search for submarines. That energy level (blue-green) has a greater penetrability than other levels and the coherency of the light beam keeps the beam intact longer.

Answer 3

It is scattered, reflected and absorbed as it encounters more water until there is none left to see by. The photons still exist, however, but not as a penetrating beam.

Light "slows down" when going through transparent material because it is being absobed and re-emitted by the atoms of the material. In between atoms, though, is empty space where it travels at its normal speed 'c'.

Answer 4

It does not slow down, but is scattered and the energy absorbed at different levels. Lights of different wavelengths penetrate deeper into the ocean before they are scattered and absorbed by water molecules.

Eventually all the visible light is absorbed. Only the wavelengths we cannot see reach the greatest depths.

Answer 5

Water diffuses light just like a prism.

Ever poke a stick or a boat paddle into the water and notice how it appears to "bend" under the surface?

Same thing - the light is being redirected.

Answer 6

Light is EM radiation. It is scattered by water molecules, with the degree of scattering dependent on the wavelength.

Answer 7

Light only travels at a constant speed through a vacuum. Mediums slow or stop it.

Answer 8

no. Those are just more powerful so they can go deeper. It doesn't change form