Notes of Chap 11
Human Eye And The Colourful World
Covered Topics
- Introduction.
- Parts of the human eye.
- Power of Accommodation.
- Defects of vision and their Correction.
- Dispersion of light by a glass prism.
- Refraction of light through a prism.
- Atmospheric Refraction.
- Scattering of light.
- Advantage of the eyes before the face. Give reason.
- Why do stars are twinkle? Give reason.
- Why we have 2 eyes for vision and not simply one? Give reason.
- Why is the colour of the clear sky blue? Give reason.
- Why will the sun look red at sunrise and sunset? Give reason.
- The sensory organ of our skull which helps us to see objects and make its images on the retina is called the human eye.
- An eyeball having it's 2.5cm or 1-inch diameter.
- It has the ability to identify the colour.
- It is located at the front part of the skull.
- Eyeball: The whole of your spherical eye including hidden parts of the eye is called eyeball.
- Aqueous humour: The clear fluid filling the area within the front of the eyeball between the lens and also the cornea is termed aqueous humour.
- Vitreous humour: The clear jellylike tissue filling the eyeball behind the lens is termed vitreous humour.
- Cornia: The transparent part that covers and protects the outer part of your eye is called the cornea.
- Pupil: A hole like structure present in the centre of the iris which allows light to enter and strike on the retina is called the pupil.
- Iris: The coloured part of the eye which controls the size of the pupil is known as iris.
- Eye Lens: A transparent and biconvex structure part of the eye that is able to refract light rays is called the eye lens. It is composed of fibrous, jelly-like material.
- Ciliary muscle: A muscle in the eye that controls how much the lens curves. Two ciliary muscles control the eye lens.
- Retina: A thin and delicate layer behind the eye that made up of light-sensitive cells is known as Retina.
- Sclera: White part of the eye that surrounded the eye and located behind the cornea is called the sclera.
- Choroid: The pigmented vascular layer of the eyeball between the retina and the sclera is known as choroid.
- Optic nerve: It is the wire-like structure that connects the eye to the brain and responsible for the transfer of visual information from the eye to the brain.
- The ability of the eye lens to adjust its focal length according to object situation and form a clear image on the retina is called the power of accommodation.
- When ciliary muscle contract then the focal length of the eye lens gets decreased
- When the ciliary muscle relaxes then the focal length of the eye lens gets increased.
- Near Point: The minimum distance point at which objects can be seen clearly is known as a near point.
- The minimum distance of clear vision is 25cm
- Far Point: The maximum distance at which objects can be seen clearly is known as far point.
- The maximum distance of clear vision is infinite.
- There are mainly three types of eye defects:
- 1. Myopia(Nearsightedness): The eye defect in which a person can see nearby objects clearly but can not see distant objects clearly this defect of the eye is known as Myopia.
- Due to elongation of eyeball image is formed in front of the retina, not on the retina
- Due to excessiveness of curvature of eye lens image form front of the retina not on retina.
- It can be corrected by using a concave lens or a converging lens.
- When we placed a concave lens in front of myopic eye it forms a virtual image of far objects at a nearby place so myopic eye is able to see that objects clearly.
- 2. Hypermetropia(Farsightedness): The eyes defect in which a person can see distant objects clearly but can not see nearby objects clearly this type of defect is known as Hypermetropia.
- Eyeball gets smaller so the image is formed behind the retina, not on retina.
- focal length gets increased so images form behind the retina.
- It can be corrected by using a convex lens.
- When we placed a convex lens in front of the eye then light rays get more converge as usually so the focal length of the lens gets decreased and image form on the retina.
- 3.Presbyopia(Old-age Hypermetropia): The eye defect in which eye accommodation power gets decreased and lens not able to adjust its focal length to form an image on the retina, this type of defect is known as Presbyopia.
- Hardening of the eye lens.
- The weakening of ciliary muscle.
- It can be corrected by using Bifocal lens
- If someone suffering from Hypermetropia then it can be corrected by using a convex lens.
- Dispersion of light: The process of splitting white light into its seven constituent colours by a glass prism is called dispersion of light.
- Spectrum: The band of seven colours formed by the dispersion of white light through a prism is called the spectrum.
- Acronym: Group of alphabets which show the sequential seven colour of the spectrum is VIBGYOR.
- Prism: A solid transparent substance which is bounded by two triangular surface and three rectangular surface and able to separate white light into seven different light band is known as the prism.
- The angle of Prism: Angle between two lateral surfaces of a prism is known as the angle of the prism or refracting angle.
- The angle of Deviation(D): The angle between the incident ray and the emergence ray is known as the angle of deviation.
- Atmospheric Refraction: Refraction made by layers of the atmosphere is called atmospheric refraction.
- Total Internal Reflection: When the light rays enter from a denser medium to a rarer medium then the angle of incidence exceeds the critical angle and the light rays reflected in the denser medium, called the total internal reflection of light.
- Critical angle: When the light rays enter from a rarer medium to denser medium then the angle of incidence where the angle of refraction is 90° this angle is called a Critical angle.
- Rainbow: Natural spectrum formed by raindrops in the sky after rains, this spectrum is called rainbow.
- Formation of Rainbow: When sunlight gets refracted two times and gets total internal reflection one time by the raindrops then it's formed a spectrum on the opposite side of the sun. Such a spectrum called rainbow.
- Particles that square measure exposed to lightweight absorb lightweight energy and re-emit lightweight completely different|in several|in numerous} directions with different intensity this development of sunshine is termed scattering of light.
- Examples: the blue colour of the sky.
- Tyndall Effects: The phenomenon of scattering of light by the colloidal particles which make paths of light visible is called Tyndall Effects.
- Note: The colour of scattered light depends on the Size of the particles.
- Ans: Front-facing eyes give us a wider range of view, detect objects and give us three-dimensional views.
- Ans: Because stars are very far from us and due to atmospheric refraction of starlight they are twinkling. When light rays enter in the earth atmosphere then starlight gets refracted by atmospheric layers and its bend starlight towards its normal so the apparent position of the star is slightly different from its actual position. So the star appears slightly above from its actual position.
- Ans: A human being has a horizontal field of view about 150° with one eye and of about 180° with two eyes. So it gives us a wider field of view. It has the ability to identify faint that's why we have two eyes instead of one.
- Ans: Because, Blue light is scattered in all directions by the tiny particles of air in Earth's atmosphere and blue is scattered more than other colours because it travels as shorter, smaller waves. That's why a clear sky colour is blue.
- Ans: Throughout sunrise and sunset sun is found terribly removed from us that the rays have to be compelled to travel a bigger a part of the atmosphere as a result of they're terribly near to the horizon. Therefore, lightweight apart from red is usually scattered away. Red light having more wavelength as compared to other light so most of the red light does not get scattered and get enters to our eyes. Hence, the sun and the sky appear red during sunrise and sunset.
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