Unit 2 - Refraction of Light Flashcards
What is refraction
when light enters a denser transparent material and changes speed and direction
Which lense focuses light?
convex
which lens diffracts light into a spectrum of colours?
prirm
which lens causes the light to diverge (go into diff directions/separate)
concave
What is the normal
dotted line drawn 90 degress to the surface it enters
what is a particle of light called
photon
What is the speed of light in a vaccume?
3x10⁸ m/s
What is the refractive index of a medium?
its the ratio of the speed of light in a vaccume to the speed of light in that medium.
What is the angle of incidence
The angle between the incident ray and the normal at the point of incidence
What is the angle of refraction
The angle between the refracted ray and the normal at the point of incidence where refraction occurs
What is the angle of reflection
The angle between the reflected ray and the normal at the point of incidence to a reflecting surface.
What is the criticle angle
it is the certain angle of incidence, where the refracted ray is bent through an angle of 90 degrees from the normal so that it just grazes the block.
What is total internal reflection (TIR)
it is when the angle of incidence is greater than the criticle angle, meaning all of the light is reflected by the boundary. No light leaves through the surface by refraction. Therefore this is called the total internal reflection, because the ray is reflected inside the block.
What are optical fibers
fibers which transfer data using light and total internal reflection. it is surrounded by glass core, cladding, buffer and jacket.
Describe the core, cladding, buffer and jacket of the optical fiber
Core
-glass with a higher index of refraction than the cladding
-carries the signal
Cladding
-Glass or plastic with a lower index of refraction than the core
Buffer
-Protects the fiber from damage
moisture
Jacket
-holds one or more fibers in a cable
Why must the cladding have lower refractive index than the core?
For TIR to occur
lower refractive index means refraction occurs until criticle angle, so the total internal reflection occurs.
What happens to the light in an optical fibre
incident angle is bigger than criticle angle, so TIR occurs, light is totaly internally reflected across the optical fibre
What are multimode optical fibres
Same as optical fibre but have multiple paths (the mode) of light travelling within them.
Advantage and Disadvantage of multimode fibres
Advantage
-less expensive to operate, install and maintain than single-mode cables
Disadvantage
-much more limited in speed and distance
What is multimode dispersion
Because different paths are taken, the modes (individual paths) have different propagation velocities (diff wave movements) Meaning that the signal does not arrive at the same time and appears distorted which is called multimode dispersion.
Why are multimode fibres only effective over short distances
so that multimode dispersion effect is smaller, as the pulses will begin to overlap.
What are monomode optical fibres
Very thin cores. Only have 1 single node which is parallel to the wire through the center. These have higher data transfer rates and can transfer data over much longer distances because there is little multimode dispersion.
what is the main difference between monomode and multimode fibres
in monomode, the core is so small that only 1 mode can pass through, No total internal reflection occurs. Angle to axis is zero.
Advantages and disadvantages of monomode fibres
Advantage
-faster and covers more distance than multimode fibre
Disadvantage
-More expensive to produce and operate than multimode fibre
Stand proud,
You are strong.
Define diffraction
The spreading out of waves when they meet obstacles such as the edges of a slit. Some of the waves energy travels into geometrical shadows of the obstacles
What type of material will cause light to refract
By entering a more dense transparent medium, or leaving a that medium to a less dense medium
