Using n2/v-n1/    u=(n1-n2)/R

    1/v-n/(R)=(1-n)/(-R)

  After solving this equation, we get Image distance v = –R
    Thus we can say that the image distance and object distance are equal and that the apparent position of dot is the same as its actual position.
    It is independent of the refractive index of the material of the sphere. Till now we have discussed refraction of light at a single curved surface either convex or concave. Let us suppose that a transparent material has two curved surfaces.
  • What happens to the light ray when a transparent material with two curved surfaces is placed in its path?
  • Have you heard about lenses?
  • How does a light ray behave when it is passed through a lens?
    • Let us learn about refraction of light through lenses.

    Lenses

        A lens is formed when a transparent material is bounded by two surfaces of which one (or) both surfaces are spherical. That is a lens is bounded by atleast one curved surface. Lenses can be of various types. Some typical lenses along with their names are shown in fig.- 6.

        A lens may have two spherical surfaces bulging outwards. Such a lens is called double convex lens (Biconvex lens, see fig.- 6(a)). It is thick at the middle as compared to edges.

        Similarly, a double concave lens is bounded by two spherical surfaces curved inwards. (Biconcave lens, see fig.- 6(d)). It is thin at the middle and thicker at the edges.

        Observe the 6(c), 6(b), 6(e) and 6(f) to understand structure of Concavo-Convex lens, Plano-Convex lens, Plano-Concave lens and Convexo-concave lens.


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