2.2 Refraction Flashcards
Define refraction
the redirection of a wave as it passes from one medium to another
What is Snell’s Law?
For light travelling from one medium to another, the ratio sin(i)/sin(r) is a constant. This constant is the refractive index of the material
Define the critical angle
the angle of incidence n a material that produces an angle of refraction of 90 degrees
When a monochromatic ray of light passes from one material to another, what happens to its speed
speed changes
When a monochromatic ray of light passes from one material to another, what happens to its wavelength?
Wavelength changes
When a monochromatic ray of light passes from one material to another, what happens to its frequency
Frequency doesn’t change
Define Total internal Reflection
the complete reflection of a light ray reaching an interface with a less dense medium when the angle of incidence exceeds the critical angle
What are the 2 conditions for TIR to take place?
- direction of light is from one material to one of lower refractive index
- the angle of incidence in the material of higher refractive index exceeds the critical angle
What is an optical fibre?
the use of a long strand of glass to send light from one end of the medium to another
Why does the intensity of the signal through an optical fibre remain constant?
None of the incident energy is lost due to the transmission of light across the boundary
What does the step-index fibre consist of
a glass core surrounded by a glass cladding, surrounded by a layer of protective plastic called a sheath
Does the core or cladding have the higher refractive index?
The core has the higher refractive index
Define modal dispersion
the difference of time taken for light to travel up a fibre along the central axis and that travelling by repeated TIR
Why is modal dispersion undesirable?
results in blurred images
How is modal dispersion prevented?
By using v thin cores so only axial mode is possible
