Chapter 5 Flashcards
What is refraction?
The bending of light at a surface/boundary because it has changed speed
Define a ray
Straight line showing direction of wave (energy direction). Should have an arrow
Define a beam
Multiple rays
Define a wavefront
A line joining all points that are in the same phase. Can be in any shape
What is true about a wavefront and an associated ray?
They are always perpendicular to each other
When looking at an axis, how do you measure all angles? (incidence, reflection etc.)
Between the ray and the normal
When does a wave not bend when it hits a surface and what happens instead?
When it hits the surface at 90 degrees. It only changes speed but carries on in a straight line
What happens to light when it goes from a less optically dense medium to a more optically dense medium?
The light will slow down and bend towards the normal
What happens to light when it goes from a more optically dense medium to a less optically dense medium?
The light will speed up and bend away from the normal
When drawing a refraction diagram, what must you always show regarding the incident ray?
Partial reflection
What happens if the boundaries that light enters are parallel in terms of the incident and emergent ray?
The incident ray will be parallel to the emergent ray
List the order of the spectrum
Red Orange Yellow Green Blue Indigo Violet
Which colour of white light bends the best and why?
Blue as it has the largest refractive index
What is the first criteria that must be met for TIR to occur?
n of material light is moving from must be > n of material light is moving into
What is the second criteria that must be met for TIR to occur?
Angle i > critical angle at that boundary
What are optical fibres used for (2 uses)
Communications - Send enclosed signals down fibre optics
Endoscopes - Medical internal examination
In optical fibres, why do you need fibres?
So that you can bend the tube
With the image channel in an optical fibre, what must happen in terms of the bundle?
It must be coherent so the image comes out correctly/ have same relative position
In fibre optics, what are the 2 components of it?
Core and cladding
Why does a fibre optic need cladding?
- Stop interference (signal leakage) between adjacent fibres
- If there are abrasions/cuts/scratches, it would touch the cladding not the signal meaning the signal wouldn’t be weakened
What is model dispersion?
When beams of light follow different paths down a fibre, so have different path lengths and the signal gets spread out
What is the solution to model dispersion?
Make the core narrower and reduce the amount the pulses spread out.
How can you make the core narrower in order to solve model dispersion?
With the cladding, otherwise the core would become narrow and brittle
What is material dispersion?
When you send white light down a fibre optic and it spreads out.
Why does material dispersion occur?
Because white light is made up of different frequencies /wavelengths. So they travel at different speeds
What is the solution to material dispersion?
Use lasers/single frequency so the pulses don’t smear out
Why is light given off a material (e.g sun)?
Because of the incandescence (giving off) of the material. This is because the material is hot
What type of light in terms of spectrum is given off by the sun?
The light produced is a continuous spectrum
What type of light in terms of spectrum is given off by a fluorescent tube?
The light given off comprises of blocks/bunches of frequencies
What type of effect is diffraction?
An edge effect
Why does diffraction occur?
Because waves interfere with themselves
What is the main application of diffraction gratings?
Spectrometers
How do spectrometers work?
The grating breaks up white light into a spectrum. Because of the first order line which is different for every wavelength.
What 2 types of spectra would be observed in a spectrometer?
Continuous or emission
What is a continuous spectrum?
A spectrum consisting of many different colours and wavelengths, but no gaps
What is an emission spectrum?
Where energy levels change due to electrons de exciting and exciting.
What happens when an electron de excites?
It gives off photons
What can the absorption spectra be used to do in terms of stars?
Identify elements in stars
Diagrams to look at:
Young's double slits Double slits (young's slits) Spectra and diffraction
