CBSE – 8th Standard Science

Light

  • We see the object only when light from an object enters our eyes. The light may have been emitted by the object, or may have been reflected by it.
  • After striking the mirror, the ray of light is reflected in another direction.
  • The light ray, which strikes surface, is incident ray. The ray that comes back after reflection is known as reflected ray.
  • The angle of incidence is always equal to the angle of reflection. This is known as the law of reflection.

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  • The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane. This is another law of reflection.
  • In 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.
  • When all the parallel rays reflected from a plane surface are not parallel the reflection is known as diffused or irregular reflection.
  • On the other hand reflection from a smooth surface like that of a mirror is called regular reflection Images are formed by regular reflection.

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  • Splitting of light into its colours is known as dispersion of light. Important parts of the eye are cornea, iris, pupil, lens, retina and optic nerve.
  • 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 (ii) rods, which are sensitive to dim light.

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  • 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.
  • Too little or too much light is bad for eyes. Insufficient light causes eyestrain and headaches. Too much light can injure the retina.
  • Always read at the normal distance for vision.
  • The most popular resource for visually challenged persons is known as Braille.

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  • 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.
  • Laws of reflection are (i) The angle of incidence is equal to the angle of reflection (ii) Incident ray, reflected ray and the normal drawn at the point of incidence to the reflecting surface, lie in the same plane.

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  • Image formed in a plane mirror undergoes lateral inversion.
  • Two mirrors inclined to each other give multiple images.
  • Splitting of light into its constituent colours is known as dispersion.
  • Important parts of the eye are cornea, iris, pupil, lens, retina and optic nerve.
  • Visually challenged persons can read and write using Braille system.
  • The world is largely known through the senses.
  • The sense of sight is one of the most important senses.
  •  Through it we see mountains, rivers, trees, plants, chairs, people and so many other things around us.
  •  We also see clouds, rainbows and birds flying in the sky. At night we see the moon and the stars.
  • The idea of number of images formed by mirrors placed at an angle to                   one another is used in a kaleidoscope to make numerous beautiful patterns.

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  • Splitting of light into its colours is known as dispersion of light. Rainbow is a natural phenomenon showing dispersion

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To sum up-

  • 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.
  • Two laws of reflection are—
  1. The angle of incidence is equal to the angle of reflection.
  2. Incident ray, reflected ray and the normal drawn at the point of incidence to the reflecting surface, lie in the same plane.
  • Image formed in a plane mirror undergoes lateral inversion.
  • Two mirrors inclined to each other give multiple images.
  • Beautiful patterns are formed in a kaleidoscope because of multiple reflections.
  • Sunlight, called white light, consists of seven colours.
  • Splitting of light into its constituent colours is known as dispersion.
  • Important parts of the eye are cornea, iris,pupil, lens, retina and optic nerve.
  • A normal eye can see nearby and distant objects clearly.
  • Visually challenged persons can read and write using Braille system.
  • Visually challenged persons develop their other senses more sharply to improve their interaction with their environment.

CBSE 8th Standard Science

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CBSE 8th Standard Science Syllabus and Revision Notes

  • Crop Production & Management
  • Microorganisms – Friends & Foe
  • Synthetic, Fibers & Plastic
  • Materials – Metals & Non-Metals
  • Coal & Petroleum
  • Combustion & Flame
  • Conservation Of Plants And Animals
  • Cell Structure And Functions
  • Reproduction In Animals
  • Reaching The Age Of Adolescence
  • Force And Pressure
  • Friction
  • Sound
  • Chemical Effects Of Electric Current
  • Some Natural Phenomena
  • Light
  • Stars And The Solar System
  • Pollution Of Air And Water