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# Refraction in water

Refraction in Water. Created by Sal Khan.

## Want to join the conversation?

• Why does speed of light slow down when it passes in a medium, be it glass or water no medium in specific..??
I am not asking for explanations for HOW but WHY....
• The exact details of what happens when light travels through a medium like water or glass is quite complex and involves a quantum mechanical description of the interaction of light with the material it is traveling through.

The speed of a photon is always the speed of light. What causes the apparent slowdown is its interaction with what it is traveling through. Light is an oscillation of electric and magnetic fields, this interacts with the electric charges of the electrons in the material causing an oscillation in the electron's electric field. The two oscillations interfere with each other causing the the combined field oscillation to propagate slower than the speed of light.

When light exits the refractive material the interference no longer occurs so the light resumes its normal apparent velocity.
• hi, as mentioned at the last part, sir khan said that the light travels straight back into the water causing an image of the coin, but however, arent the light bend when they travel back into the water? If take it that the light is directly shown into the water, then 0 degrees incidence = refraction angle is 90 degrees law will be violated, i am so unclear with this, and lastly, the light that i meant here is the observer's eye please comment!~
• The dotted lines shown are simply where the brain thinks the light rays are coming from, because the light rays are coming out a a different angle, so it seems as though they are actually coming from a different point. Again, the trace-backs are just an optical illusion, not a real light ray, so they don't refract for the simple reason that they never existed in the first place, it is just what the brain thinks.
• Which colour light penetrates to deepest depth in water and why?
• red colour light penetrates water and air the best and can travel the longest. that is why radio waves which have a long wavelength like red light are used for satellite communication. so waves with longer wavelength can penetrate substances better but since they have low frequency, they cannot harm living tissue.
• At , Sal says that the left side is faster than the right side. What about a ray that is coming perpendicular to the ground? Will it stay straight as it goes from water to air?
• Yes, it will stay straight. Think of Snell's law: The angle of incidence will be 0 degrees. As you might know, the sine of 0 degrees is 0. So the second side of Snell's law would also have to be equal to 0. We know that the refraction index of the 2nd medium is not zero, and hence we are led to the conclusion that the angle of refraction has to be 0.
• Does different gases also affect the direction and speed of light?
• Anything that causes the speed of light to change will affect the direction, whether it be gas, liquid or solid.
• will more refraction take place when the water is cold?
• Yes, because cold water is more dense than hot water
• I have seen ships appearing as if they float in air, which is called looming. Can the concept of looming be linked to the idea of refraction? If yes, then how?
• Really cool question, you are on the right track! I don't know enough about this to explain too in depth but the basic concept involves two specific conditions: temperatures of water vs air, and the location of the ship with respect to the horizon. The relative density of air changes (vertically) when a layer of warm air flows over cold water: it has the lowest density near the water (because it's cooler) and increases in density as you get higher (farther away from the water: warmer). This also suggests that the air near the surface has a lower index of refraction while the upper layers of air have a higher index of refraction. When the ship is at or below the horizon, the change from light traveling through air with a low index to traveling through air with a high index means that light will bend towards normal. The ship therefore not only appears as though it is floating above the surface of the water but will also appear magnified! Hope that helps!
• what is the cause of refraction of light ?
• All waves refract when they go from one medium to another one where the speed of the wave is different from the first one
• Can this happen only for light? As light is just a type of electromagnetic radiation, would other electromagnetic radiations reflect, refract and disperse?
Thanks