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  Sign convention for spherical lenses Sign convention of spherical lens is similar to the sign convention of the spherical mirrors.         Object is placed on the left of the lens. It means to say that light must passes through the lens from left to light. All measurements of distance are taken from the optical centre of the lens. The focal length of a convex lens is positive. And the focal length of the concave lens is negative. All distance measured above the principal axis are positive. All distance measured below the principal axis are negative. All the distance measured in the direction of incident rays are positive. All the distance measured in the direction opposite to that of the incident rays are negative.     Lens formula and magnification   Lens formula provides the relationship between object distance (u) ,   image distance (v) and the focal length (f). lens formula is applicable of both concave lens and convex lens. The image generated by th

  Refraction by spherical lenses Refraction means to state that the change of the direction of the parallel beam of ray of lights when it passes through one medium to another medium. The image formed by the convex lens is enlarged. And the image formed by the concave lens is diminished.   Lens :--               A lens is a transparent material bounded by two surfaces of which one or both surfaces are spherical. It means to say that a lens is bounded by at least one spherical surface. And other surface is plane surface. Or we can say that lens is a transparent material or   glass bounded by the two spherical surfaces and is used for magnifying the objects. The working of lens is mainly based on the refraction of ray of lights when they passes through it. There are two types of lens. A concave lens and convex lens. concave surface  convex surface   Convex lens :--                       A convex lens is the spherical lens having two spherical surfaces bulging outward

                      The refractive index The refractive index:-- When a ray of light travels from one transparent medium into another medium, the change of direction takes place in a given pair of media is called as refractive index. the refractive index can be linked with the important physical quantity, the relative speed of propagation of light in different media.   It means speed of light propagates with different speeds in different media. Speed of light is faster in vacuum with speed   of 3 * 10 8   meters/second. but in the air, the speed of light is 2.98   * 10 8 meters/second. It means speed of light in air   is compared less as compared with speed of light in the vacuum. And the speed of light in glass and water is less than the speed of light in vacuum. The refractive index determine the path of light is bent or refracted, when entering any medium.                          The refractive index is expressed as the   degree of the change of direction   of the ligh

  Refraction of light Refraction of light:--                                   Refraction of light is the bending of light, When ray of light travel through one medium to another medium. The speed of light is maximum in the vacuum. During refraction , the frequency of light remains same but the speed of light and wavelength changes. Refraction of light observed in many places in our daily life. When any object is   immersed in the water. These object appears closer than the real position. Some natural phenomena including rainbows and mirages is also observed due to refraction of light.     Some examples can be taken:-- When a coin is poured inside the filled water bucket, then the coin is appeared slightly raised above its actual position due to refraction of light.   Refraction through a rectangular glass slab:--   To understand the phenomenon of the refraction of light through a glass slab, we should take a paper sheet and place a glass slab over the white paper

  Sign convention for reflection by spherical mirrors To deal with the reflection of light by spherical mirror, we have to follow a set of conventions is known as the new cartesian sign convention. The pole of the spherical mirror is taken as the origin. The principal axis of the spherical mirror is taken as the X-axis of the coordinate system. The object is always placed to the left of the spherical mirror. It means to say that the ray of light coming from the object falls on the spherical mirror from the left handed side. All the distances parallel to the principal axis are measured from the pole of the spherical mirror. All the distances which are measured to the right (along +ve X-axis) are taken as the positive. All the distance which are measured to the left of the origin (along -ve X-axis ) are taken as the negative. The height measured perpendicular to the principal axis and are upward to the principal axis (along +ve Y-axis) are taken as positive. The height