Have you ever wondered why a straw appears to be disconnected when placed in water?

In a vacuum, light travels at 3.0 x 10 8 m/s, Light travels at different speeds in different materials or mediums. while in water light travels at 2.26 x 10 8 m/s. This is because different materials have different optical densities. Basically the less dense a substance is the faster light can travel through it

 Order the following mediums from lowest optical density (1) to highest optical density (4): In which of those 4 mediums would light travel the fastest? In which of those 4 mediums would light travel the slowest? #1 #2 #3 #4

 Is it possible for light to travel any faster than it does in a vacuum? NO!

When light travels from one medium to another it changes speed and bends. The bending of light is called refraction. Refraction occurs as light passes across the boundary between two different mediums. For example, when light travels from water to air, it bends because it speeds up as it enters the air.

When a ray of light passes from one transparent medium into another of greater optical density, the ray will bend toward the normal. When light travels from one transparent medium into another one of lesser optical density, Note: The normal is a line drawn at a right angle (90°) to the surface. All angles are measured from this normal line. the light will bend away from the normal.

 Arthur must aim the arrow at a position on the water below where the fish appears to be. Since light refracts away from the normal (water to air), the refracted ray when extended backwards passes over the head of where the fish actually is. If Arthur were to throw the arrow towards the image of the fish, he would miss the fish entirely.

Light travels at different speeds in different materials. The index of refraction (n) is defined as the speed of light in a vacuum divided by the speed of light in the medium. You can determine the index of refraction (n) by doing a simple calculation.

c = 3.0 X 10 8 m/s n cannot have a value of less than 1 The higher the value of n the slower the speed of light in that medium. because light cannot travel faster than in a vacuum.

SubstanceIndex of Refraction (n) Vacuum Air (we use 1 to simplify things) Ice1.31 Water1.33 Glass (crown)1.52 Glass (flint)1.61 Diamond2.42 Acrylic1.49 Vegetable oil1.48

Example 1: Calculate the index of refraction for glass (crown). Given: speed of light in a vacuum c = 3.00 x 10 8 m/s speed of light in glass (crown) v = 2.00 x 10 8 m/s n glass (index of refraction of glass (crown))Unknown: Equation: Solve: n glass = c / v n glass = 3.00 x 10 8 m/s = x 10 8 m/s The index of refraction for glass (crown) is 1.5 Statement : [Note: the number is dimensionless, since the units cancel each other out.]

Example 2: Calculate the speed of light in ethyl alcohol. Given: speed of light in a vacuum c = 3.00 x 10 8 m/s index of refraction of ethyl alcohol n ethyl alcohol = 1.36 v (ethyl alcohol)Unknown: Equation: Solve: v = c / n ethyl alcohol v = 3.00 x 10 8 m/s = 2.2 x 10 8 m/s 1.36 The speed of light in ethyl alcohol is 2.2 x 10 8 m/s Statement :

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