Current Affairs 8th Class

Category : 8th Class

Light

·                     When light falls on a surface, a part of it reflects back. If light falls on a polished and shiny surface, most of its part reflect back in the same medium. There are two types of reflection of light ?

·                     Regular reflection takes place when a ray of light is incident on a polished smooth surface like a mirror. Here the reflected ray of light moves only in a fixed direction.

·                     Irregular reflection or diffused reflection takes place when a ray of light is incident on a wall or wood, which is not smooth or polished.

·                     In case of irregular reflection, the different portions of the surface reflect the incident light in different directions and thus no definite image is formed, but the surface becomes visible. It is commonly known as scattering of light.

·                     Light always follows the law of reflection, whether the reflection occurs off a curved surface or off a flat surface. Two laws of reflection are:

§  The angle of incidence is equal to the angle of reflection.

§  Incident ray, reflected ray and the normal drawn at the point of incidence to the reflecting surface, lie m the same plane.

·                     Image formed by a plane mirror is laterally inverted i.e. the left of the object appears in right and the right of the object appears in left.

·                     Multiple images are formed when two plane mirrors inclined to each other

·                     A kaleidoscope is a cylinder made with two or more mirrors. Light reflecting between these mirrors produces multiple virtual images of stunning beauty.

·                     Sunlight, called white light, consists of seven colours.

·                     When white light is made to pass through prism, it splits into its constituent colours. This phenomenon is known as dispersion.

·                     Eye is an important organ which helps us in seeing the beauty of nature. The important parts of the eye are cornea/ iris, pupil, lens, retina and optic nerve.

·                     Retina contains two types of nerve cells ?

·                     Cones are sensitive to bright light while rods are sensitive to dim light.

·                     There are no sensory cells present at the junction of the optic nerve and the retina, so no vision is possible at that spot. This is called the blind spot.

·                     A normal eye can see nearby and distant objects clearly.

·                     The most comfortable distance at which one can read with a normal eye is about 25 cm. This is called distance of distinct vision.

·                     Some persons cannot see nearby objects while some others cannot see distant objects so clearly. These defects can be corrected with suitable corrective lenses.

·                     The three main defects of eyes are - myopia (near sightedness), hypermetropia (far sightedness) and astigmatism.

·                     Braille is a tactile writing system used by the blind and the visually impaired to read and write.

·                     The other senses of visually challenged persons are more developed to improve their interaction with their environment.