Human Eye Flashcards
Why is diff in colour of the sun in sun during sunset
Light from near the horizon passes thru thick layers of air and longer dist
Light frm overhead passes thru shorter distance. At noon sun appears white and little of blue is scattered. Near the horizon most of the blue lights scattered. Therefore the light that reaches our eyes are of longer wavelengths and appears reddish in colour
Where is red light uses in and why
Red light is uses in danger signals as it has a longer wavelength. It is scattered by for or smoke
Why does the sky appear dark to flight passengers
Scattering of light is not prominent at such heights.
Why does the sky appear blue
Molecules of air have fine particles which have a shorter wavelength than that of visible light.
These are more effective in scattering of light in shorter wavelengths of blue than scattering of light in longer wavelengths of red. Red has a wavelength of 1.8 times greater than blue and therefore scatter blue more than red. If there was no atmosphere there wld be no scattering
What is tyndall effect give example
When a beam of light strikes fine particles the path of the beam becomes clear. Scattering of light by colloidal particles gives rise to tyndall effect. Sunlight passes thru canopy in forest
Explain scattering of light. What does colour depend on
Phenomena due to which the light changes its direction on striking an obstacle. Colour depends on size of particle
Fine particles - short wave length vice versa
Particle v large - while light
Effects of atmos ref on sunrise and sunset
2 mins diff bw both
delayed sunset advanced sunrise
Apparent flattening of suns disc and sunset –> same phenomenon
Ref nb for figure
Planets don’t twinkle why?
Planets are much closer to the earth and are considered as extended sources. If we consider them as large point sized sources of light avg will be 0
therefore nullifying the effect
Twinkling of stars is due to…
explain the process
what is twinkling effect
Atmospheric refraction
Undergoes refraction before entering earth. AR occurs in a medium of gradually changing refractive index. Since atmos bends starlight toward normal apparent position seems to be higher than it actually is. This position is not stationary but is changing slightly bcuz of physical cond of earth.
As the path of rays varies position of starlight fluctuates and flickers. Sometimes they appear brighter or fainter –> twinkling effect
What is rainbow explain with figure
Figure in nb
It is a natural spectrum which occurs due to dispersion of tiny droplets. These tiny droplets act like small prisms. Rainbow is always towards the dir of sun. They refract and disperse incident sunlight, reflect internally and again refract it after coming out of droplet.
What did Isaac newton do
He was the first to use a glass prism to obtain spectrum of sunlight –> he placed an inverted identical spectrum to obtain white light again
Which light bends least and most
Red
Violet
White light splits into a band of colours…what is a spectrum
VIBGYOR
Band of coloured components of light beam
What is angle of prism and angle of deviation
Explain when light ray bends toward normal and bends away from normal
Angle between its 2 lateral faces
Emerging ray bends towards dir of incident ray
Light ray towards normal - when light enters from air to glass
vice versa
Contrast between prism and rectangular glass slab
Rectangular slab - emergent ray and extended incident ray parallel while when we pass a Ray of white light from prism, it splits into seven colours.
On passing through glass slab, a light ray gets refracted and emerges out the glass slab in a direction parallel to the direction of incident ray. This occurs due to the presence of a lateral shift. Whereas, on passing through a glass prism, light rays get deviated in a direction not parallel to the incident ray.
Cure for blindness what are the conditions
Corneal transplantation Eye donors can belong to any sex or age removed withing 4 to 6 hrs after death Itll 15 mins max Cannot donate eyes - aids, hepatitis , leukaemia
What is cataract
Old age - when crystalline lens turns milky
Near point of healthy eye… what is least dist vision
25 cm
Min dist in which n eye can see clearly without strain
When does fl increase and decrease
Muscles relax - lens becomes thin - fl increases
Muscles contract - lens becomes thick - fl decreases
What is accommodation
Ability of lens to adjust focal length
How can eye lens curvature be modified what happens when it is modified
eye lens curvature can be modified by ciliary muscles
fl also changes
What happens upon activation of light sensitive cells
Generate electrical impulses upon illumination… these impulses go to brain via optic nerve which interprets and processes info
Function of pupil
Controls light rays entering eye
Iris location and function
Behind cornea, dark muscular diaphragm which controls size of pupil
Diameter of eyeball?
2.3 cm
Function of cornea
Refraction of light rays
Thin membrane which forms a bulge on front surface of eye?
Cornea
Image formation on light sensitive screen
Retina
What is presbyopia
Why do some require bi focal lens and what is bi focal lens
Power of acc decreases with ageing –> gradual weakening of ciliary muscles , Difficult to see nearby obj without corrective glasses
When ppl are suffering frm both myopia and hypermetropia –> bi focal lens
Consists of concave ( upper part for distant vision) and convex ( lower part for near vision) lens.
Hypermetropia also known as….
Explain hypermetropia
what is the reason for its defect and what is the correction
Far sightedness, cannot see near by objects clearly requires reading material beyond 25 cm
Near point farther than 25 cm
Eye ball has become too small
Focal length too long
What is Myopia also known as
Explain Myopia
Why does this defect arise
Near sightedness, Cannot see farther objects clearly. Far point near to infinity
Elongation of eyeball, Excessive curvature of eye lens
Corrected using concave lens
