Points to Remember-Class 10 -Science- Physics-Chapter 11:The Human Eye And The Colourful World

Class 10 -Science-Points to Remember- Physics-Chapter 11:The Human Eye And The Colourful World

IMPORTANT POINTS TO BE REMEMBER  

◆ Cornea : A transparent spherical membrane which refracts light into the eye is called cornea. 

◆ Iris : A dark muscular diaphragm that controls the size of the pupil is called iris.

◆ Pupil : A small circular opening in the centre of the iris is called pupil. Pupil appears black because no light  if reflected from it. 

◆ Eye lens : A converging lens made of a transparent jelly-like proteinaceous material behind the pupil is called the eye lens. 

◆ Retina : The inside surface of the real (back) part of the eye ball where the light which enters the eye is focussed is called retina. The surface of the retina consists of about 125 million light-sensitive receptors. These receptors are called rods and cones. The rods are sensitive to the intensity of light, while cones are sensitive to the colour of light. 

◆ Colour blindness : It is a defect of the eye due to which person is not able to distinguish between certain colours. Colour blindness is a genetic disorder. 

◆ Near point : The nearest point up to which an eye can see clearly is called its near point 

◆ Far point : The farthest point up to which an eye can see clearly is called its far point. For a normal eye, the far point is at infinity. 

◆ Least distance of distinct vision : The minimum distance up to which an eye can see clearly is called the least distance of distinct vision. For a normal eye of an adult, the least distance of distinct vision is 25 cm. 

◆ Accommodation power of the eye : The property due to which the eye lens is able to change its focal length is called accommodation of the eye. When the eye is focussed on any distant object, the ciliary muscle is most tense (strained).  

◆ Myopia (shortsightedness) : The defect on eye due to which eye is not able to see the distant objects clearly though it can see the nearby objects clearly is called myopia or shortsightedness.   Myopia is caused by a decrease in the focal length of the eye lens. It can be corrected by using spectacles made from concave lenses of suitable focal length.  

◆ Dispersion of white light : The process of splitting white light into its seven constituent colours is called dispersion of white light. The band of seven colours is called spectrum of visible light.   Rainbows are formed due to the dispersion of white light by small droplets of water hanging in the air after the rain.

◆ Rainbow : Rainbow is a band of seven colours across the sky produced due to the dispersion of white light by small raindrops hanging in the air after the rain. 

◆ Atmospheric refraction : The optical density of our atmosphere decreases with altitude. Thus a ray of light entering any layer