Eye and Colourful World Notes PDF

 HUMAN EYE Sense organ that helps us to see. Located in eye sockets in skull. Diameter of Eye is 2.3 cm (Size of eye remains same throughout our whole life) Parts of Human Eye Parts of HUMAN EYE 1. Cornea – It is the outermost, transparent part. It provides most of the refraction...

 HUMAN EYE Sense organ that helps us to see. Located in eye sockets in skull. Diameter of Eye is 2.3 cm (Size of eye remains same throughout our whole life) Parts of Human Eye Parts of HUMAN EYE 1. Cornea – It is the outermost, transparent part. It provides most of the refraction of light. 2. Lens – It is composed of a fibrous, jelly like material. Provides the focused real and inverted image of the object on the Retina. This is convex lens that converges light at Retina. 3. Iris – It is a dark muscular diaphragm that controls the size of the pupil. 4. Pupil – It is the window of the eye. It is the central aperture in Iris. It regulates and controls the amount of light entering the eye. Parts of HUMAN EYE 5) Ciliary Muscles – They hold the lens in position and help in modifying the curvature of lens. 6) Retina – It is a delicate membrane having enormous number of light sensitive cells. 7) Optic Nerve – It transmits visual information from retina to Brain. 8) Blind Spot – The point at which the optic nerve leaves the eye. Parts of HUMAN EYE 9) Aqueous Humour – Between the cornea and eye lens, there is a space filled with transparent liquid is called the aqueous humour which helps the refracted light to be focused on retina. It also provides nutrition to eye. 10) Vitreous Humour – Space between eye lens and retina is filled with a liquid called Vitreous Humour. Far Point of Eye – Maximum distance to which eye can see clearly, is called far point of eye. - For a normal eye, it’s value is Infinity Near Point of Eye – Minimum distance at which an object can be seen most distinctly without any strain is called the least distance of distinct vision. - For a normal eye, it’s value is 25cm Power of Accommodation The process by which certain muscles (called ciliary muscles) function to change the focal length of the eyes so that the image is clearly formed on the retina is called accommodation of the eye. If the object in consideration is at a distance, for the image to form at the retina, the focal length has to be large. Here, the ciliary muscles relax, thereby thinning the eye lens. The focal length increases and the image is formed perfectly on the retina. Similarly, in the case of near-lying objects, the ciliary muscles contract and thereby thickening the lens. This causes a reduction in the focal length for ideal image formation. Range of human vision is from 25 cm to infinity Case 1) To see far Objects Ciliary Muscles - Relaxed Eye Lens – Thin Focal length - Increase Case 2) To see near Objects Ciliary Muscles - Contract Eye Lens – Thick Focal length - Decrease How our Eyes Focus? Myopia Myopia (near sightedness) A myopic person can see nearby objects clearly but cannot see distant objects clearly. Image is formed in front of Retina. Causes of Myopia - - Excessive curvature of eye lens - Stretching of eye ball  Correction 1. It is done by using concave lens of appropriate power. a) In a myopic eye, image of distant object is formed in front of the retina (not on retina)  Correction b) The far point (F) of a myopic eye is less than infinity.  Correction c) The concave lens placed in front of eye forms a virtual image of distant object at far point (F) of the myopic eye Hypermetropia Hypermetropia (far sightedness) - Affected person can see far objects clearly but can’t see nearby objects clearly. - The near point of eye moves away. - Image is formed behind Causes of Hypermetropia - the retina. - Focal length of eye lens becomes too long. - Eye ball becomes too small.  Correction It is done by using convex lens of appropriate power. a) In a hypermetropic eye, image of distant object is formed behind the retina (not on retina)  Correction b) The near point (N) of a hypermetropic eye is more than 25cm  Correction c) Correction of hypermetropia. The convex lens placed in front of eye forms a real image of near object on Retina. Correction Advantage of eyes in front of the face - It gives a wider field of view. - It provides three-dimensional view PRISM Dispersion of Light - The splitting of white light into its components due to different bending ability for colors when it pass through prism is called DISPERSION OF LIGHT. Total Internal Reflection When light travels from denser medium to rarer medium with angle of incidence greater than critical angle then the refracted ray instead of emerging out again goes into the same medium. This is known as total internal reflection. Two conditions: i. light travels from denser medium to rarer medium ii. ii. the angle of incidence is greater than critical angle Rainbow Formation  How a Rainbow forms? Sun emits 7 Colour light in its visible range Why do sky appears blue? Blue Light is scattered more than other colors because it has shorter wavelength. Tiny atmospheric particles can scatter only shorter wavelengths. Why do sun appear more reddish during sunrise and sunset? Light rays have to travel a larger part of the atmosphere because they are very close to the horizon. Therefore, light other than red is mostly scattered away. Why DANGER signals are usually represented by RED COLOUR? Why YELLOW COLOUR to school bus?  Why do celestial body appear slightly raised from their position? Due to atmospheric refraction. Q. What is the reason behind 2 minutes early sunrise and 2 minutes delayed sunset? Ans. It is because of atmospheric refraction. When the Sun is slightly below the horizon, the light coming from it travels from less dense to more dense air and is refracted downwards. Q. Why do stars twinkle but planets do not? Stars twinkle because of turbulence in the atmosphere of the Earth. As the atmosphere churns, the light from the star is refracted in different directions. Planets do not twinkle because they are not very far away from us like stars