refraction. light tends to travel in straight lines if you need to bend light or shine it into...
DESCRIPTION
Fibre Optics Fiber optics (optical fibers) are long, thin strands of very pure glass about the diameter of a human hair. Core - Thin glass center of the fiber where the light travels Cladding - Outer optical material surrounding the core that reflects the light back into the core Buffer coating - Plastic coating that protects the fiber from damage and moistureTRANSCRIPT
Refraction
Lighthttp://arrowheadradio.com/images/fiber-optics.jpg
Tends to travel in straight lines
If you need to bend light or shine it into difficult-to-reach places, optical fibres can be used
Fibre Opticshttp://static.howstuffworks.com/gif/fiber-optic-fiber-edit.jpg
Fiber optics (optical fibers) are long, thin strands of very pure glass about the diameter of a human hair.
Core - Thin glass center of the fiber where the light travels
Cladding - Outer optical material surrounding the core that reflects the light back into the core
Buffer coating - Plastic coating that protects the fiber from damage and moisture
Refractionhttp://thescienceroom.pbworks.com/f/brokpen.jpg
Light also bends when it passes from one medium into another such as from water to air
The pencil appears to bend because light rays change direction as the move between mediums
Refraction in a Poolhttp://www.wildpackets.com/images/compendium/FDRflct.gif
You may have stood by a pool and seen an object on the bottom that you want to pick up
When you dived in to get the object, it wasn’t where it appeared to be
Why? This happens because the light rays change
direction at the surface of the water as they pass between the water and the air
When we view the refracted light rays we assume they have traveled in a straight line
If you trace the light rays back in a straight line you will find that they don’t lead to the object
How Light Refracts If light strikes a new
medium at and angle it will bend
Think of a light beam as the leading edge of a wave, the part that strikes the surface first slows down
How Light Refractshttp://optics.mbhs.edu/snells-law/image1.JPG
As light enters the plastic block it slows down and refracts
As light leaves the block and enters the air it speeds up and refracts
Light does not refract inside the block, only when changing mediums
Speed of Lighthttp://2.bp.blogspot.com/_2ii88_lzmW0/TSSZcbuLLOI/AAAAAAAAAMM/x_iuQyjc5Ak/s1600/
speed_of_light_highway.jpg
In a vacuum, light travels at almost 300 million m/s or 3.0X108 m/s
Light travels almost that fast in air
The more dense the medium, the slower light can travel through it.
The Index of Refraction
The amount by which a transparent medium decreases the speed of light is indicated by a number called the index of refraction
The larger the refractive index, the more the medium decreases the speed of light
The refractive index of the speed of light in a vacuum (and approx. air) is 1.00
Calculating the Index of Refraction
Index of refraction =
Speed of light in a vacuumSpeed of light in medium
Or
n = c/v
The refractive index of a medium, n, is calculated by comparing the speed of light in the medium, v, with the speed of light in a vacuum, c.
PracticeRead example problems page 438
Do all 6 calculations page 438
Angles of Refraction
Angles of refracted light rays are usually measured from the normal, drawn at 90º to the surface where the light ray crosses between two media
Low to High Refractive Index
When light travels from air, with a low refractive index to water, with a high refractive index, it bends toward the normal
Low to High Refractive Index
When light travels from water, with a higher refractive index (denser medium) to air, with a lower refractive index (less dense medium), it bends away from the normal
Dispersionhttp://www.educationalelectronicsusa.com/l/images/light-XVa.gif
The splitting of a ray into its component colours is known as dispersion of light and the band of colours is known as a spectrum
Rainbows The most common type
of dispersion is in the formation of a rainbow
When sunlight passes through a rain drop, some of the light is refracted, once on entering and again on exiting the drop
Both refractions cause separation of the white light
Snell’s Law A formula that
uses the index of refraction to calculate the new angle that a ray will take as a beam of light strikes the interface between two media
Calculations with Snell’s Law
n1 sin 1= n2 sin 2
Let the indices of the two media be n1 and n2
Let the angle of incidence be 1
Let the angle of refraction be 2
PracticeRead example problems page 441 - 442
Do all 6 calculations page 441 - 442
Total Internal Reflectionhttp://www.hsc.csu.edu.au/senior_science/core/info_systems/9_4_6/Laserpath.gif
Sometimes light does not pass from one medium to another, but stays within the medium
This happens in the case of fibre optics
Total Internal Reflection http://labspace.open.ac.uk/file.php/6211/t305_002i.jpg
Light reflects completely off the inside wall of a denser medium (higher index of refraction) rather than passing through the wall into a less dense medium (lower index of refraction)
RECALL!
When light passes from a denser material into a less dense material, the light refracts away from the normal
The Critical Angle
As the angle of incidence increases, the angle of refraction increases
At the critical angle, the refracted ray of light follows a path exactly along the surface of the water
Past The Critical Angle If the angle of incidence is increased past
the critical angle, the light ray is reflected not refracted
Mirages
Both total internal reflection and refraction play a role in forming a mirage
Mirages Light rays pass through layers of air with
progressively lower indices of refraction, eventually the light is totally internally reflected
Mirageshttp://www.islandnet.com/~see/weather/graphics/photos/infmirg2.gif
The End