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A concave mirror of focal length 20 cm and a convex lens of focal length 10 cm are kept with their optic axes parallel but separated by 0 . 5 cm as shown in the figure. The distance between the lens and mirror is 10 cm . An object of height 3 mm is placed on the optic axis of lens at a distance 15 cm from the lens. Find the length of the image formed by the mirror in mm .

Correct answer

3

Step-by-step solution

For image formed by the lens 1 v 1 - 1 - 15 = 1 + 10 ⇒ v 1 = + 30   c m i.e. 20   cm behind mirror For mirror 1 v 2 + 1 20 = 1 - 20 ⇒ v 2 = - 10   cm Overall magnification = 30 - 15 × 10 20 = - 1 Length of image =   1   ×   3   =   3   mm

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