Chapter Review:
- The human eye is one of the most valuable and sensitive sense organs.
- An image on a light-sensitive screen called the retina. Light enters the eye through a thin membrane called the cornea. It forms the transparent bulge on the front surface of the eyeball.
- The eyeball is approximately spherical in shape with a diameter of about 2.3 cm.
- Iris is a dark muscular diaphragm that controls the size of the pupil.
- The pupil regulates and controls the amount of light entering the eye. The eye lens forms an inverted real image of the object on the retina.
- The ability of the eye lens to adjust its focal length is called
accommodation. - The minimum distance, at which objects can be seen most distinctly without strain, is called the least distance of distinct vision. It is also called the near point of the eye.
- The farthest point upto which the eye can see objects clearly is
called the far point of the eye. - The near point is about 25 cm.
- The farthest point is infinity for a normal eye.
- The crystalline lens of people at old age becomes milky and
cloudy. This condition is called cataract. - A human being has a horizontal field of view of about 150° with one eye and of about 180° with two eyes.
- There are mainly three common refractive defects of vision. These
are (i) myopia or near-sightedness, (ii) Hypermetropia or farsightedness, and (iii) Presbyopia. - A person with myopia can see nearby objects clearly but cannot see distant objects distinctly .
- A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly.
- The power of accommodation of the eye usually decreases with ageing.The near point gradually recedes away. They find it difficult to see nearby objects comfortably and distinctly without corrective eye-glasses. This defect is called Presbyopia.
- Eyes must be removed within 4-6 hours after death.
- The angle between its two lateral faces is called the angle of the prism.
- The emergent ray bend at an angle to the direction of the incident ray. This angle is called the angle of deviation.
- The splitting of light into its component colours is called dispersion.
- The Sun is visible to us about 2 minutes before the actual sunrise, and about 2 minutes after the actual sunset because of atmospheric refraction.
- The red light has a wavelength about 1.8 times greater than blue light.
- Scattering of light causes the blue colour of sky and the reddening of the Sun at sunrise and sunset.
