CBSE Class 10 Science 2017 · Paper 531 · Question 36

Light - Reflection and Refraction 2 marks Medium

A student determined the focal length of a convex lens as

20

cm. He then obtained the image of an object using this lens. The image formed was inverted, equal in size and real.

(i)What is the position of the object in front of convex lens ?
(ii)What will be the position of image formed ? Draw ray diagram to justify your answer.

Answer

The object is at $2 F_{1}$ , 40 cm from the lens, and the real, inverted, same-size image forms at $2 F_{2}$ , 40 cm behind it.

(i) The object is at

2 F_{1}

, that is

40

cm in front of the lens (

u = - 40

cm). (ii) The image forms at

2 F_{2}

40

cm behind the lens on the other side (

v = + 40

cm); it is real, inverted and of the same size, and the ray diagram shows the two rays meeting there.

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