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A screen is placed 90cm from an object. ...

A screen is placed 90cm from an object. The image of the object on the screen is formed by a convex lens at two different locations separated by 20cm. Determine the focal length of the lens.

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21.4cm
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NCERT GUJARATI-RAY OPTICS AND OPTICAL INSTRUMENTS-EXERCISES
  1. Answer the following questions: (d) Does the apparent depth of a tan...

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  2. Answer the following questions: (e) The refractive index of diamond ...

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  3. The image of a small electric bulb fixed on the wall of a room is to b...

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  4. A screen is placed 90cm from an object. The image of the object on the...

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  5. (a) Determine the 'effective focal length' of the combination of the t...

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  6. At what angle should a ray of light be incident on the face of a prism...

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  7. A card sheet divided into squares each of size 1 mm^(2) is being viewe...

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  8. (a) At what distance should the lens be held from the figure in Exerci...

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  9. What should be the distance between the object in Exercise 9.24 and th...

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  10. Answer the following questions: (a) The angle subtended at the eye b...

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  11. Answer the following questions: (b) In viewing through a magnifying ...

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  12. Answer the following questions: (c) Magnifying power of a simple mic...

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  13. Answer the following questions: (d) Why must both the objective and ...

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  14. Answer the following questions: (e) When viewing through a compound ...

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  15. An angular magnification (magnifying power) of 30X is desired using an...

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  16. A small telescope has an objective lens of focal length 140cm and an e...

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  17. (a) For the telescope described in Exercise 9.28 (a), what is the sepa...

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  18. A Cassegrain telescope uses two mirrors as shown in Fig. 9.30. Such a ...

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  19. Light incident normally on a plane mirror attached to a galvanometer c...

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  20. Figure 9.34 shows an equiconvex lens (of refractive index 1.50) in con...

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