Refraction Of Light


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       A lens formula may be defined as the formula which gives the relationship between the distance of image (v), distance of object (u), and the focal length (f) of the lens. It may be written as:

Principal Axis Concave Lens

       Where,   v   =   Distance of image from optical centre of lens
                     u   =   Distance of object from optical centre of lens
       and         f   =   Focal length of lens

       The lens formula is applicable both in convex lenses and concave lenses.

Test Your Understanding and Answer These Questions:

  1. Define lens formula.

  2. Is lens formula applicable only for convex lens?

  3. An object 5 cm high is held 25 cm away from a converging lens of focal length 20 cm. Draw the ray diagram and find the position, size and nature of the image formed.

  4. A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.

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