- Light is reflected from all surfaces.
- Regular reflection takes place when light is incident
on smooth, polished and regular surfaces.
- Diffused/irregular reflection takes place
from rough surfaces.
-Reflection from a smooth surface like that of a mirror
is called regular reflection.
- The angle between the normal and incident ray is called
the angle of incidence (Úi). The angle between the normal and the
reflected
ray is known as the angle of reflection (Úr)
- Law
of reflection:
·
Angle
of incidence is always equal to the angle of reflection.
·
The
incident ray, the normal at the point of incidence and the reflected ray all
lie in the same plane.
- An image formed by a mirror the left of the object
appears on the right and the right appears on the left. This is known as lateral inversion.
Designers of wallpapers and fabrics and artists use kaleidoscopes to get ideas for new
patterns.
- Eyes: The dark muscular
structure behind the cornea is called iris. In the iris, there is a small
opening called the pupil. The size of the pupil is controlled by the iris. The
iris is the part of that eye which gives it its distinctive colour.
When we say that a person has green eyes, we refer
actually to the colour of the iris. The iris controls the amount of light
entering into the eye.
- The lens focuses light on the back of the eye, on a
layer called retina.
- Retina contains several nerve cells. Sensations felt by
the nerve cells are then transmitted to the brain through the optic nerve.
- There are two kinds of cells
(i) cones, which are sensitive to bright light and
Cones sense colour.
(ii) rods, which are sensitive to dim light.
At the junction
of the optic nerve and the retina, there are no sensory cells, so no vision is
possible at that spot. This is called the blind spot.
- Louis Braille, himself a visually challenged person,
developed a system for visually challenged persons and published it in 1821.
- Braille system has 63 dot patterns or characters. Each
character represents a letter, a combination of letters, a common word or a
grammatical sign. Dots are arranged in cells of two vertical rows of three dots
each.
- Diwakar, a child prodigy has given amazing performances
as a singer.
- Mr. Ravindra Jain, born completely visually challenged,
obtained his Sangeet Prabhakar degree from Allahabad. He has shown his
excellence as a lyricist, singer and music composer.
- Mr. Lal Advani, he himself visually challenged,
established an Association for special education and rehabilitation of disabled
in India. Besides, he represented India on Braille problems to UNESCO.
- Helen A Keller, an American author and lecturer, is
perhaps the most well known and inspiring visually challenged person. She lost
her sight when she was only 18 months old. But because of her resolve and
courage she could complete her graduation from a university. She wrote a number
of books including The Story of my Life (1903).
For key points of other chapters from Science VIII NCERT book you can buy IAS prelims 2016 study module -3 ( click here )