In a vacuum (void of molecules), light travels at 3.0 x 108 m/s,

Light travels at different speeds in different materials or

mediums.

while in water light travels at 2.26 x 108 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.vacuum space

#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 when light enters a translucent or transparent material.

Refraction occurs as light passes across the boundary between two different mediums.

For example, when light travels from air into glass, it bends because it slows down as it enters the glass from air.

the ray will bend toward the normal.

When a ray of light passes from one transparent medium into another of greater optical density,

When light travels from one transparent medium into another one of lesser optical density,

 

the light will bend away from the normal.

Note: The normal is a line drawn at a right angle (90°) to the surface. All angles are measured from this normal line.

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 108 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.

Substance Index of Refraction (n)

Vacuum 1.0000Air (we use 1 to simplify things) 1.0003

Ice 1.31Water 1.33

Glass (crown) 1.52Glass (flint) 1.61Diamond 2.42Acrylic 1.49

Vegetable oil 1.48

Example #1:

The speed of light of glass(crown) is 2.00 x 108 m/s. Calculate the index of refraction for glass.

[Note: the number is dimensionless, since the units cancel each other out.]

Example #2:

If the index of refraction of ethyl alcohol is 1.36, calculate the speed of light in ethyl alcohol.

Example 1: Calculate the index of refraction for glass (crown).

Given: speed of light in a vacuum c = 3.00 x 108 m/sspeed of light in glass (crown) v = 2.00 x 108 m/snglass (index of refraction of glass

(crown)) Unknown:

Equation:Solve:

nglass = c / v

nglass = 3.00 x 108 m/s = 1.5

2.00 x 108 m/sThe 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 diamond.

Given: speed of light in a vacuum c = 3.00 x 108 m/sindex of refraction of diamond ndiamond = 2.42v (diamond) Unknown:

Equation:Solve:

v = c / ndiamond

v = 3.00 x 108 m/s = 1.24 x 108 m/s

2.42The speed of light in diamond is 1.24 x 108 m/s

Statement :

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