45-49;Refraction/Eye/Optical Instruments/microscope/colour vision Flashcards
refraction
bending of light rays at interfaces where speed of light changes
speed of light in free space c=3x10^8 m/s
when it enters transparent medium IE glass/air it travels at a lower speed - if propagation speed is perpendicular to boundary - no visible effect accompanies change in speed
refraction makes deep clear bodies of water appear shallow
deflection
when light moves from air into glass, speed decreases and ray bends depending on change it speed
index of refraction
always > or = 1
optical properties of substances
lens
optical device that focuses or disperses light beam by refraction
convex lens = parallel light rays strike CxL focuses to a point at fixed distance f beyond lens
concave lens = parallel light rays strike CeL and diverges so they focus at distance f behind lens = -ive sign
converging lens = form real images of object
image formation by the eye
light from object strikes eye - passes cornea (where refraction occurs w/ fixed focal length) + crystalline lens (changes shape to alter focal length via ring of ciliary muscles) - transparent vitreous humor forms real image on retina - retina nerve endings transmit electric impulses to brain via optic nerve
distant object = muscles relax = lens held in strained position by ciliary fibres to focus
close object = stronger lens required = ciliary muscles contract = fibres loosen = lens is round = shortens focal point = increases refracting ability
common vision defects
focal length of eye lens is too short = light rays focus before reaching retina = blurred vision on retina/myopia/nearsightedness = corrected by diverging lens = rays diverge slightly before entering eye
focal length of eye lens too long = light focuses greater distance than to retina = hyperopia/farsightedness = converging lens
astigmatism = lens has diff focal length for light ray = strikes it in diff planes
simple optical instruments
additional lens/collection of lens used to aid lens of eye = provide larger image of object to to view inaccessible areas
simple magnifier
simple converging lens = larger image on retina
compound microscope
uses 2 lens; objective and eyepiece
focusing ability provided by movement of both lens to magnify small objects
opthalmoscope
instrument used to view retina of eye
simplest form consists of light source, mirror w/ aperture
light reflected from mirror into subject’s eye to illuminate retina = reflected light rays rendered parallel by eye lens when passing out = focused by observer’s eye = clear image of retina
fibre optics
light enters small fibre = passes along fibre by multiple internal reflections = illuminates tract ahead
complicated system developed for bronchoscopes (lungs/air passages), cystoscopes (urethra/bladder) to view internal tracts of body
colour vision
beam of white light passed through prism = separated into coloured bands by refraction due to n=f(f) so diff freq bent at diff angles
3.8 x 10^-7 - 7.7x10^-7m
1Angstrom = 10^-10m
how eye sees colour
retina of eye contains rods and cones = light-sensitive nerve endings
rods = single type of cell, provide monochromatic vision, mainly night time, little colour discriminating ability
cones = discriminates between colours, less sensitive to light, densely packed in fovea
