L1- fundamentals of geometrical optics Flashcards
what is light?
. light is a form of radiant energy
. comes from sun or candle
. smallest quantity of energy that can be transported ( photon )
. wave-particle duality- consider light as a particle using a wave theory
what are the main properties of light?
. velocity . wave length . frequency . speed ( 3x10^8) m/s . polarization . intensity
what does the sun emit?
white light - which is a combination of all colours on the electromagnetic scale.(400( ultraviolet(shorter) ) -700nm( Infrared- longer) )
what are the 2 basic rules of geometrical optics ?
. light travels in the forms of rays that are coming from source of light
. a ray of light travels in a straight line until it meets an optical boundary
how would you see a red pencil?
. the sun emits white light
. dyes on surface of pencil only reflect back red light and absorb all other colours
. only red rays are re-emitted and reach observer eye
what does monochromatic mean?
single wavelength
what does poly chromatic mean ?
many wavelength
what is black ?
absence of colour
what happens when light crosses an interface between two transparent media?
when light travels from air to glass
the wavefronts are closer together in glass, which suggests slowing down of light within the medium
light will travel slower in glass because its more optically dense than air
(v is smaller than c)
what is the relation between density and speed of light ?
the more optically dense a medium (than air )is the slower light will travel through it
why do rays bend?
rays bend as they cross an optical surface between two transparent media with two different optical density
what happens to the wave front as it crosses the interface?
. bottom part of wavefront will hit this speed restriction earlier than top part of wavefront
. as wave front crosses interface the bottom part is travelling slower than the top part and will lag down
. when wavefront crosses boundary both top and bottom part will travel at same speed
why do wave front tilt when crossing air-glass interface?
.wave front has been tilted because of the uneven slowing as it crosses the air-glass interface
. light travels in a different direction after crossing interface
what is refraction?
bending of light rays when they cross an optical surface between media with different optical density
why does a pencil look bent in water
. light rays from the bit of pencil under water will intersect in a different location than light rays from portion of pencil that extends above water
. this is why bit of pencil under water appears to be in a different location that portion of pencil that extend above water
what is snell’s law of refraction ?
n sin i = n' sin i' n= refractive index before refraction i= angle of incidence n'= refractive index after refraction i'= angle of refraction
where is angle i ?
angle between incident ray of light ( ray travelling towards surface ) and normal to surface
where is normal line drawn ?
drawn where light intersects surface
where is angle i’ ?
angle between refractive ray of light ( ray travelling away from surface ) and normal
what is refractive index of air?
1
what does a higher refractive index mean?
higher refractive index more dense a material
what does snell’s law tell us ?
- the amount of refraction we get
- how much a ray bends depends on the difference between refractive indices in their two medium
how are prisms used in optometry?
. to alter apparent location of an object
. sometimes an image what one eye sees is not in line with what the other eye sees
. a lens with prism will bring image into binocular synch with image seen by other eye
. used to treat double vision
how are objects viewed through a prism displaced?
. objects viewed through prism are displaced through apex of prism away from base
what is the amount of displacement in a prism dependent on ?
.the size of angle of apex
greater angle=thicker prism
. thicker prism= stronger correction and displaces object to greater degree
. thinner prisms= weaker amount of correction and displace object to lesser degree
why does blue light refract more than red light?
. shorter wavelength
. higher refractive index
What is the property of light that determines colour?
wavelength
What should waves and rays do?
waves and rays must intersect at right angles
what is visible light ?
- part of electromagnetic spectrum and ranges from 400nm to 700nm
- lies between IR and UV
- human eye can detect
where do rays and wavefront intersect ?
rays and wavefront intersect at right angle to one another
What are photons?
individual particles of light
What is the intersection of a ray and a wavefront?
always a right angle
What do most objects have?
diffuse surfaces whihc means light rays are scattered in all directions
What is a transparent medium ?
A transparent medium is a medium which transmits all wavelengths in the visible spectrum without reflecting or absorbing any.
-Air and water are the most common transparent media
