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What is the focal length of a convex len...

What is the focal length of a convex lens of focal length `30 cm` in contact with a concave lens of focal length `20 cm`. Is the system a converging or a diverging lens ? Ignore thickness of the lenses.

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A diverging lens of focal length 60 cm
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NCERT TAMIL-RAY OPTICS AND OPTICAL INSTRUMENTS-EXERCISES
  1. A beam of light converges to a point P. A lens is placed in the path o...

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  2. An object of size 3.0 cm is placed 14 cm in front of a concave lens of...

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  3. What is the focal length of a convex lens of focal length 30 cm in con...

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  4. A compound microscope consists of an objective lens of focal length 2....

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  5. A person with a normal near point (25 cm) using a compound microscope ...

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  6. A small telescope has an objective lens of focal length 144 cm and an ...

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  7. (i) A giant refracting telescope at an observatory has an objective le...

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  8. Use the mirror equation to deduct that : (a) an object between f and...

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  9. A small pin fixed on a table top is viewed from above from a distance ...

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  10. a.Figure shows a cross-section of a 'light pipe' made of glass fibre o...

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  11. Answer the following questions : Does the apparent depth of a tank o...

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  12. Answer the following questions : Does the apparent depth of a tank o...

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  13. Answer the following questions : Does the apparent depth of a tank o...

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  14. Answer the following questions : Does the apparent depth of a tank o...

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  15. Answer the following questions : Does the apparent depth of a tank o...

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  17. A screen is placed 90 cm from an object. The image an object on the sc...

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  18. a) Determine the effective focal length of the combination of the two ...

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

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  20. A cardsheet divided into squares each of size 1 mm^(2) is being viewed...

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