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Q. 13. An object 2 cm high is placed at a distance of 64 cm from a white screen. On placing a convex lens at a distance of 32 cm from the object it is found that a distinct image of the object is formed on the screen. What is the focal length of the convex lens and size of the image formed on the screen? Draw a ray diagram to show the formation of the image in this position of the object with respect to the lens.

Sol.
Size of the Object, h1 = + 2 cm
Object distance, u = – 32 cm
Image distance, v = 64 – 32 = + 32 cm (Real)
Focal length of the Convex lens, f = ?
Size of the image, h2 = ?
According to lens formula

Q.14. The position of three elements A, B and C in the Periodic Table are shown below :

Giving reasons, explain the following :
(a) Element A is a non-metal.
(b) Element B has a larger atomic size than element C.
(c) Element C has a valency of 1. 3

Science 2008 Question Papers Class X
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