HUMAN EYE

We know that eye is the sense of organ which produces the sensation of sight. It consist of following parts a)CORNEA it is a thin membrane which cover the eye b) PUPIL it is the opening in the center of the iris to allow light to enter the eye. c)IRIS it is the part of eye which controls the amount of light entering the eye by changing the size of the pupil. d)RETINA it is a light sensitive screen inside the on which image is formed e)OPTIC NERVE  It transmit the electrical signal to brain e) CRYSTALLINE LENS :It helps to focus light into the retina. f)CILIARY MUSCLES : These muscles are attached to the eye lens that modify the shape of the lens which leads to the variation in focal length .g)VITREOUS HUMOUR :It is clear gel that fill the space between the lens and retina of the eye ball it provides the shape to eye. h)AQUEOUS HUMOUR :It is the fluid inside the front part of eye between cornea and eye lens

FUNDAMENTAL FACTS : POWER OF ACCOMMODATION is the ability  of eye lens to focus  near and far objects clearly on retina by adjusting it’s focal length it is limited for  least distance of distinct vision is 25cm and for distance it is infinity.

PERSISTENCE OF EYE : The sensation of the object continues in the eye for about 1/16 second in the other words it is the impression of the object seen by eye remain on retina for1/16 second  even the object is removed in front of eye.

DEFECTS OF VISION  a)MYOPIA/ SHORT SIGHTNESS  in this kind of defect a person can see near distance object clearly but fail to see far distance object  because image formed before retina this defect is caused due to  eye lens become too curved and eye ball gets elongated  it can be corrected by using concave lens of suitable focal length

 

HYPERMETROPIA / FAR SIGHTEDNESS  in this defect a person can see far distance object very clearly but unable to see near distant objects the image of the objects is formed behind the retina  this defect is caused when focal length of eye lens become too long and eye lens become too small. This defect can be corrected when convex lens of suitable focal lenght is used to form the image on retina.

HUMAN  EYE DEFECT  ; a) PRESBYOPIA in this defect the ciliary muscles gets weaken with age of a person and eye lens become rigid due to which  power of accommodation of eye gets loosen  this defect can be removed by using bi focal lens of suitable focal length

b) ASTIGMATISM  in this defect a person cannot simultaneously cannot see both the horizontal and vertical  views of the objects clearly  cornea is not perfectly spherical in shape. this defect can be removed by using  cylindrical lens of suitable focal length.

NEWTON  was the first person who proved that white light is made of seven constituent colours  he passed the sunlight through the prism to form the band of seven colours  He tried to split the colours further by putting another prism ahead in inverted form but failed to get any more   colours  finally concluded that white light is made up of seven colours.

DISPERSION OF LIGHT :When white light passes through a glass prism it splits into seven constituent colours to form the band of seven colours this is called  dispersion of light

Spectrum is the band of seven colours formed due to dispersion of white light through the prism.

Acronym is a group of alphabets that represent the sequential of colours in spectrum as VIBGYOR .

angle of deviation = 1/ wave length   red having largest wave length least deviated whereas violet having shortest wave length  deviates most . Each colour has definite wave length so angle of deviation is different for each colour therefore the spectrum is formed it is to be noted  any light that form spectrum  similar to sunlight is white light

PRISM  is a pyramidal piece of glass  having two triangular bases three rectangular lateral surfaces  the angle between two adjoining surfaces is called angle of prism

ANGLE OF DEVIATION : is the angle between incident ray and emergent ray

TOTAL INTERNAL REFLECTION  When a ray of light passes from denser to rare medium it bends away from normal  at specific angle of incidence the angle of refraction is of 90degree to the normal making an interface to the both the medium this angle of incidence  is called  critical angle if angle of incidence become more than critical angle the refracted ray  goes back in the same medium this is called total internal reflection

Condition for total internal reflection  a) Light should obliquely from dense medium to rare medium b) angle of incidence must be greater than critical angle.

NATURAL EXAMPLE  a) Formation of Rainbow :After rain small water droplets remain suspended in air these droplets behave like glass prism when sunlight enters the rain drops it is refracted and disperses reflect internally and refracts again when it comes out of rain drops it reaches to our eye in seven colour refractive index of hot air is less than the cool airs. b) An object placed behind the fire appear to be flickering because air  above hot surface becomes hot and rises, the space is occupied by cool air the refractive index of hot air is less than the cool air and physical condition changes regularly so refractive index also changes  light comes from different direction due to which fluctuation in apparent position of objects. c) Stars when seen near the horizon appear slightly higher than their actual position due to atmospheric refraction because  the refractive index of earth atmosphere increases from top to bottom so light coming from the star near the horizon has to travel rare to denser medium bends towards the normal and appears higher. d) Advance of sun rise /sun set : The sun  appear about  two minutes earlier or it continue appear  two minutes  later because when  the sun  is below  horizon the rays have to pass from rare to denser medium bends away from normal appear higher from actual position  e)  Stars are very far so they  behave as point source of light  since the physical condition of earth atmosphere changes continuously the light  from the stars appear to come from different directions this create  fluctuation of  apparent position of star  moreover the light coming from the stars also vary due to changing refractive index of atmosphere  so it appear to be twinkle . f) spreading  effect of light is various  direction colloid particles is called scattering effect  wand when light passes through  a  colloid it’s path becomes visible this is called Tyndal effect  scattering is inversely proportional to wavelength therefore violet ,indigo and blue scattered most and sky appear to blueish.