Cornea – a transparent membrane throughwhich light entersPupil - anaperture throughwhich light entersthe eye’s lens- the pupil canincrease in size toadjust theintensity of lightentering the eye.
Ciliary muscle – ligaments that control the curvature ofthe lensRetina – locatedat the back ofthe eye- light is focusedby the lens on theretina where rodsand cones convertthe light intoelectrical signalsOptic nerve –transmits theseelectric signals tothe brain
Fovea – an areaof exceptionallyacute vision- each cone isconnected to adifferent nervefiberCones areconcentrated atthe center androds are foundprimarily along theedges of theretina
Rods detect light, dark and grays.Scotopic vision – used at night or in low light rods are used distinguishes shapes but not colors, little detail Cones detect color and are only sensitive to bright light. Photopic vision – used during the day, cones are mainly used, shaped and colors are distinguished
There are three types of cones, for short, medium and longwavelengths.
The lens of the eye is a converging lens which means itfocuses the light at a point (focal point). It cannot focuson two objects at different distances at the same time. Depth of vision Near point The range of The closest point on which the human eye can focus without straining. About 25 cm distances that can but depends greatly on age. be seen clearly. Far point The largest distance the eye can focus on without straining. Considered to be infinityfor a normal eye (a few meters)AccomodationThe ability of thelens to change itsshape to focus ondifferent distances.
Cones are sensitive to the primary colors:red, blue and green.Secondary colors (cyan, magenta and yellow)are composed of the primary colors two at atime.
Color blindness – most common kind is the inability todistinguish between red and green.Partial color blindness – one type of cone is notfunctioning and only those colors dependent on thatcone cannot be distinguished. Complete color blindness – two types of cone are not functional and no color can be distinguished.
DiffractionDiffraction is the spreadingout of a wave as it goes pastan obstacle or through anaperture.When the wavelength is smallcompared to the aperture theamount of diffraction isminimal.
b is the angle to the first minimum (radians!) is the wavelength of the light usedb is the size of the opening
A single slit of width 1.5 m is illuminatedwith light of wavelength 500.0 nm. Findthe angular width of the centralmaximum. = 39o
ResolutionThe ability to distinguish between twoobjects. Because light diffracts, two distant stars that are close together may appear to be one object.
The Rayleigh criterionTwo sources are just resolvedif the central maximum of onesource falls on the firstminimum of the other.
Diffraction pattern due to a circular opening bUseful in optical devices where b is the diameter of the opening.
The camera of a spy satellite orbiting at 200 kmhas a diameter of 35 cm. What is the smallestdistance this camera can resolve on the surfaceof the earth (assume a wavelength of 500 nm). b 1.22 x 5 x 10-7)/0.35 = 1.74 x 10–6 rad S=R = 2 x 107 x 1.74 x 10-6 = 0.34 m
The headlights of a car are 2 m apart. Thepupil of the human eye has a diameter of about2 mm. Suppose that light of wavelength 500nm is being used. What is the maximumdistance at which the two headlights are seenas distinct? b = 3 x 10–4 rad R = s/ m
PolarizationOnly light that is oriented on the sameplane as the filter will pass through
Polarization by reflectionWhen light reflects off asurface, the reflected ray ispartially polarized (“glare”).The degree to which it ispolarized depends on theangle of incidence.
Brewster’s Law The Brewster angle is the angle of incidence that will create reflected light that is 100% polarized. n = tanCalculate the Brewster angle for light incidenton the surface of water (n = 1.33). = 53.1o
A polarizer is a material with a molecularstructure that only allows a specificorientation to pass through.An analyser is a polarizer that is used todetermine if light is polarized.
The intensity (brightness) of light passingthrough an analyzer is dependent on theangle the polarizer makes with theorientation of the light. I = Iocos2Calculate in terms of Io the intensity of light passing through ananalyzer when = 40o.I = .6 IoGraph of Intensity vs angle.
Doppler effect• The frequency of a wave changes when the source of the waves is in motion or the observer is in motion• Higher pitch when the source is approaching, lower pitch when the source is moving away• Higher pitch when the observer is approaching, lower pitch when the observer is moving away
Moving sourceThe frequency of a car’s horn is 200 Hz when the car is at rest. Whatfrequency will be heard if the car is approaching the observer at 30m/s? The speed of sound in air is 330 m/sf = 220 Hz
The frequency of a car’s horn is 200 Hz when the car is at rest. Whatfrequency will be heard if an observer is approaching the car at 30m/s? The speed of sound in air is 330 m/sf = 218 Hz
Light from distant stars is also affected by the Doppler Effect. v/ f f= c f = change in freq f = emitted freq v = speed of source c = speed of light Hydrogen in a distant galaxy emits light of wavelength 658 nm. The light received on earth is measured to be 689 nm. Find the speed of the galaxy. v = 1.4 x 10 7 m/s