the human eye? The human eye uses light and enables us to see objects colourful world around us. The human eye . Eye removal takes only minutes. The Human Eye and the Colourful World For Class 10 Formulas Download PDF. 1. The Human Eye It is a natural optical instrument which is used to see the. State one role of ciliary muscles in the human eye. Give an example of optical phenomena which occurs in nature due to atmospheric.
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Free PDF download of Class 10 Science Chapter 11 - Human Eye and Colourful World Revision Notes & Short Key-notes prepared by expert Science teachers. CBSE class 10 Science Chapter 11 Human Eye and Colourful World notes in PDF are available for free download in myCBSEguide mobile. #Blood: blood vessels and lymph: life processes: ncert class science: biology:cbse syllabus. by Amritanshu Keshri.
It is a kind of defect in human eye due to which a person can see near objects clearly but he can not see the distant objects clearly. Myopia is due to i excessive curvature of cornea.
Hypermetropia Long sightedness: It is a kind of defect in human eye due to which a person can see distant objects properly but cannot see the nearby objects clearly. It happens due to i decrease in power of eye lens i. It is a kind of defect in human eye which occurs due to ageing.
It happens due to i decrease in flexibility of eye lens. It is a kind of defect in human eye due to which a person cannot see focus simultaneously horizontal and vertical lines both. Due to the membrane growth over eye lens, the eye lens becomes hazy or even opaque.
This leads to decrease or loss of vision. The problem is called cataract. It can be corrected only by surgery.
Dispersion of white light by a glass prism: The phenomenon of splitting of white light into its seven constituent colours when it passes through a glass prism is called dispersion of white light.
The band of seven colours is called spectrum. Composition of white light: White light consists of seven colours i. Monochromatic light: Light consisting of single colour or wavelength is called monochromatic light, e. When someone enters a dim room, very little light is available to the eye. The iris then makes the pupil to gradually expand open up to allow more light to enter the eye. This process takes some time. That is why the pupil takes a little time to adjust itself to dim light.
What is meant by the far point, near point, and the least distance of distinct vision? For a normal eye, the far point is at infinity. The near point for a healthy normal eye of an adult lies about 25 cm from the eye.
The least distance of distinct vision is thus equal to the distance between the eye and its near point. For a normal eye of an adult, the least distance of distinct vision is about 25 cm. This distance usually increases with age. A normal eye can see both the distant and the nearby objects clearly.
For a clear vision, the image of any object must fall on the retina. For a person, the distance between the retina and the eye lens is fixed. So, the distance of the image v from the eye lens is fixed.
For objects at different distances, the values of u are different. So, to get the images at the same v, the focal length of the eye lens should be different.
The eye can focus the images of all the objects, distant or nearby, at the same place on the retina by changing the focal length of its lens.
The eye lens can change its focal length by changing its thickness with the help of its ciliary muscles. The property due to which eye lens is able to change its focal length is called accommodation of the eye.
When the eye is focussed on distant objects objects at infinity , the ciliary muscle is fully relaxed. When the ciliary muscle is in the relaxed state, the thickness of the lens is minimum and the focal length maximum: equal to the distance of the retina from the eye lens. Therefore, the parallel rays coming from any distant object are focussed on the retina, and the object is seen clearly.
When the eye is focussed on a nearby object, the ciliary muscle gets strained tense. Tension in the ciliary muscle decreases the focal length of the eye lens by slightly increasing its thickness in such a way that the image is formed on the retina.
Thus, the eye focuses on the nearby objects by tensing the ciliary muscle. These adjustments in the focal length of the eye lens take place so fast that we do not realise such changes.
What is meant by the limit of accommodation? The eye can accommodate only up to a limit. A normal eye can accommodate up to the least distance of distinct vision: about 25 cm for a healthy adult.
The objects which are very close to the eye produce blurred image. Thus, a normal eye can accommodate objects lying between infinity and the least distance of distinct vision. What is the range of vision? The range of distance over which the eye can see clearly is called its range of vision. A normal human eye can see objects clearly which lie between infinity and the least distance of distinct vision.
So, the range of vision of a normal healthy human eye is from infinity to the least distance of distinct vision, i. What is meant by the persistence of vision?
The image formed on the retina of the eyes is not permanent. It also does not fade away instantaneously after the object is removed or we have stopped seeing the object. The phenomenon of persistence of vision is made use of in motion-picture projection or cinematography.
A sequence of still pictures are recorded on a film by a movie camera. This recorded film is projected on a screen at the speed of about 24 pictures per second. Due to the persistent of vision, the successive images on the screen merge smoothly into one another giving an impression of continuity. In this way, we are able to see the pictures in motion.
How do we see the colours We see an object only when its image is formed at the retina. Our retina has a large number of light-sensitive cells. These cells are of two shapes - rods and cones. The rod-shaped cells respond to the intensity of light, i. The cone-shaped cells respond to the colours.
How Pupil Works? Here the pupil of an eye provides a variable aperture, whose size is controlled by iris a When the light is bright : Iris contracts the pupil, so that less light enters the eye. Pupil opens completely, when iris is relaxed. Persistence of Vision : It is the time for which the sensation of an object continue in the eye.
Power of Accommodation The ability of eye lens to adjust its focal length with the help of ciliary muscles is called accommodation. Eye lens becomes thin 1. Eye lens becomes thick 2.
Increases the focal length 2. Decreases the focal length 3. Enable us to see distant object clearly 3. Enable us to see nearby object clearly Near point of the Eye It is 25cm for normal eye. The minimum distance at which object can be seen most distinctly without strain. For point of the Eye It is infinity for normal eye. It is the farthest point upto which the eye can see objects clearly Defects of Vision and their Correction 1. Cataract : The image can not be seen distinctly because eye lens become milky and cloudy.
This condition is known as cataract, it can cause complete or partial loss of vision. This can be corrected by surgical removal of extra growth cataract surgery.
Myopia : Near Sightedness A person can see nearby object clearly, but cannot see distant object distinctly. Image formed in front of the retina. The Reason of defect Excessive curvature of eye lens means Eye lens be comes thick and its focal length decreases.
Elongation of the eye ball. Correction Corrected by using a Concave Lens of appropriate power.
Hypermetropia Far — Sightedness A person cannot see nearby object clearly, but can see distant object distinctly. Image formed at a point behind the retina The Reason of defect 1. Increase in focal length of the eye lens Thin eye lens 2. Eye ball has become too small.