(a) Define the power of lens.
(b) Draw a ray diagram for formation of image of an object situated at a point in between $2 f_{1}$ and $f_{1}$ distances from the optical centre of the concave lens and write the nature of the image formed.
(c) What happens when light is falling perpendicular to an interface of two media?

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Solution

(a) The power of a lens is defined as the reciprocal of its focal length.

(b) The ray diagram is shown for the formation of image of an object situated at a point in between $2 f_{1}$ and $f_{1}$ distances from the optical centre of the concave lens.
A diminished, virtual and erect image formed is between focus $f_{1}$ and optical centre $O$ .

(c) When light falls perpendicular to an interface of two media, it enters into the second media without any refraction. Here the angle of incidence is $0 °$ . For such angle of incidence, bending of light at the interface of the media does not take place.

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