Refraction of light Flashcards
What is Snells law?
At the boundary between any two given materials, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant.
What is the equation to find refractive index?
n= speed of light in a vacuum/ speed of light in the medium (n=c/v).
What are the two equations for refractive indexes?
n1v1=n2v2 or n1sinθ1=n2sinθ2.
Why is diamond shiny?
Because it has a high refractive index of 2.42.
When can total internal reflection occur?
When light moves from a more optically dense material to a less optically dense material causing a change in speed.
Describe total internal reflection
Where the incident angle is greater than the critical angle and so the light ray is reflected back into the water. θ1= θ2.
What happens when the incident angle is equal to the critical angle?
The light ray passes along the surface of the boundary.
What happens when the incident angle is less than the critical angle?
The light wave refracts from the normal as it emerges from the water.
Describe how optical fibres work
Optical fibres use total internal reflection. The refractive index of the cladding is less than the core and so the rays of infrared light are reflected back into the core as long as their angle is greater than the critical angle.
What are monomode fibres?
Optical fibres where the core diameter is so small that the only possible path through the fibre is parallel to the axis.
What are multimode fibres?
Optical fibres with a core that is thick enough for each pulse to travel by many paths involving total internal reflections, with the infrared light traveling in zig zag paths.
What are the advantages of using monomode fibres?
They are better suited to long distance communication as their signal can travel 50x further than multimode fibres.
The paths at different angles to the axis are at different lengths so data doesn’t travel on different paths that would arrive at different times, so data isn’t muddled.
How does using angles close to the critical angle minimise multimode dispersion?
Cutting down the range of path lengths
Less likelihood of overlapping
What are optical fibres?
A long, thin cylindrical core of glass, encased in a cladding of glass with a lower refractive index.
What are the advantages to using multimode fibres?
They result in the transmitted signal being subjected to very little distortion.
The preservation of the shape of the signal means that rapidly changing and complicated waves that carry lots of data can be sent and accurately received.
