On completion of this lesson, students should be able to:

  • Explain the laws of refraction.
  • Draw the ray diagram of concave and convex lenses.
  • Show the uses of lenses in our daily life.
  • Explain the defects of vision and their remedy.
  • Explain the working of optical instruments such as camera, telescope and microscope.


Laws of Refraction

The phenomenon of bending of light as it passes from one medium to another medium is called refraction of light. The refraction is caused due to change in velocity of light as it passes from one medium to another medium. This note contains different definitions regarding a lens and also shows how light bends when it passes through concave or convex lens.

Microscope and Telescope

The instrument, which are used to produce an image of an object by using a lens or a combination of lenses, are called optical instrument. Examples are a Photographic camera, microscope, telescope, etc. This note explains the normal working mechanism of telescope and microscope and briefly explains about the photographic camera: is an optical instrument that is used to record a permanent image of an object on a photographic film.

Human Eye

Conjunctive, ciliary body, aqueous, iris, cornea, pupil, lens, optic nerve, macula, retina, sclera, vitreous, etc. are the parts of human eye. This note has information about, the working principle of human eye and also the defects arise when the proper focus of light is not at the retina.