This PSEB 10th Class Science Notes Chapter 11 The Human Eye and The Colourful World will help you in revision during exams.
PSEB 10th Class Science Notes Chapter 11 The Human Eye and The Colourful World
→ The eye is the most useful natural optical instrument.
→ Distance between near and far points is called accommodation.
→ The least distance of distinct vision for a normal eye is 25 cm.
→ The retina is the most sensitive part of the eye.
→ Rods present on the retina are sensitive to the intensity of light and cones are sensitive to colours of light.
→ The most sensitive part of the retina where the image of the object is formed is called the yellow spot.
→ The focal length of the eye lens can be varied with the help of ciliary muscles.
→ The defects of the eye are myopia, hypermetropia, presbyopia, astigmatism, and colour blindness.
→ Colour blindness cannot be cured while myopia can be corrected by using a diverging (say a concave) lens of suitable focal length.
→ Hypermetropia can be corrected by using a converging (say a convex) lens of suitable focal length. For correcting presbyopia, bifocal lenses are required. Astigmatism is corrected by using a cylindrical lens.
→ Eyes can be donated after death. Even a person using spectacles, contact lens or who have been operated on for cataract or suffering from hypertension can also donate eyes.
→ The cornea of dead persons’ eyes is removed within 6 hours of death and transplanted in blind persons’ eyes.
→ Eye Lens: It is a convex lens made of a fibrous jelly-like substance on the retina of which the real and inverted image of the object is formed.
→ Cornea: It is a transparent membranous bulged out coating in the front part of the eyeball through which light enters the eye, is called the cornea.
→ Iris: The structure just behind the cornea which controls the size of the pupil is called the iris.
→ Myopia: It is the defect of the eye in which the near objects are clearly visible while distant objects are not distinctly visible.
→ Hypermetropia: The defect of the eye in which the distant objects are clearly visible whereas the near objects are not.
→ Retina: It is a delicate membrane having a large number of light-sensitive cells that become active on being illuminated produce electric signals carried to the brain.
→ Near Point: The shortest distance at which if an object is placed is seen clearly without any strain, is called the near point of the eye.
→ Far Point: The farthest point at which an object is placed is seen very clearly.
→ Cataract: The formation of a milky translucent layer on the crystalline lens is called a cataract which results in less visibility and ultimately complete loss of eyesight.
→ Least Distance of Distinct Vision: The minimum distance at which if the object placed can be seen very clearly is called the least distance of distinct vision.
→ Colour Blindness: That defect of the eye in which a person can see clearly but can not distinguish colours is called colour blindness.
→ Persistence of Vision: The sensitiveness of the retina which retains the existence of image for \(\frac{1}{216}\)th of a second even after when it is actually removed.
→ Presbyopia: With aging, the power of accommodation of eyes decreases, and the person cannot read. This defect is due to the weakening of the ciliary muscles.
→ Bifocal Lens: Defect of the eye in which a person suffers both from myopia and hypermetropia. Such a person needs a bifocal lens consisting convex lens (lower part) to see near objects and a concave lens (upper part) to see far-off objects.
→ Prism: It is a piece of a transparent refracting medium having two triangular and three rectangular surfaces. These surfaces are inclined to each other.
→ The angle of Prism: The angle between two surfaces of the prism is called the angle of prism.
→ Tyndal Effect: If a strong beam of light is passed through a colloidal solution, the path of the beam becomes visible when seen with a microscope placed at a right angle. This effect is called the Tyndal effect.