CBSE Class 10 Science 2020 · Paper 31/3/1 · Question 22

Light - Reflection and Refraction 3 marks Medium

The diagram given below shows an object O and its image I. Without actually drawing the ray diagram, state the following :

(i)Type of lens (Converging / Diverging)
(ii)Name two optical instruments where such an image is obtained.
(iii)List three characteristics of the image formed if this lens is replaced by a concave mirror of focal length ‘ $f$ ’ and an object is placed at a distance ‘ $f /2$ ’ in front of the mirror.

Answer

Converging lens; magnifying glass and microscope; the concave mirror gives a virtual, erect image, magnified to twice the object's size.

(i) Converging lens (a convex lens). (ii) Magnifying glass (simple microscope) and microscope. (iii) The image is virtual, erect and magnified: with

u = - \frac{f}{2}

the mirror formula gives

v = + f

(behind the mirror) and

m = + 2

, so the image is twice the size of the object.

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