Q65.A plane convex lens of refractive index 1.5 and radius of curvature 30 cm is silvered at the curved surface. Now this lens has been used to form the image of an object. At what distance from this lens an object be placed in order to have a real image of the size of the object? (1) 20 cm (2) 30 cm (3) 60 cm (4) 80 cm
What This Question Tests
This question requires calculating the equivalent focal length of a silvered plano-convex lens (acting as a concave mirror) and then determining the object distance for a real image of the same size.
Concepts Tested
Formulas Used
1/F_eq = (2/f_lens) + (1/f_mirror)
1/f = (n-1)(1/R1 - 1/R2)
f_mirror = R/2
1/v + 1/u = 1/F_eq
📚 NCERT Sections This Tests
9.7 — Double-Convex Lenses Are To Be Manufactured From A Glass Of
Physics Class 12 · Chapter 9
9.7 Double-convex lenses are to be manufactured from a glass of refractive index 1.55, with both faces of the same radius of curvature. What is the radius of curvature required if the focal length is to be 20cm?
9.19 — A Screen Is Placed 90Cm From An Object. The Image Of The Object On
Physics Class 12 · Chapter 9
9.19 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.
9.20 — (A) Determine The ‘Effective Focal Length’ Of The Combination Of
Physics Class 12 · Chapter 9
9.20 (a) Determine the ‘effective focal length’ of the combination of the two lenses in Exercise 9.10, if they are placed 8.0cm apart with their principal axes coincident. Does the answer depend on which side of the combination a beam of parallel light is incident? Is the notion of effective focal length of this system useful at all? (b) An object 1.5 cm in size is placed on the side of the convex lens in the arrangement (a) above. The distance between the object and the convex lens is 40 cm. Determine the magnification produced by the two-lens system, and the size of the image.
📋 Question Details
- Chapter
- Ray Optics
- Topic
- Lenses and Mirrors Combination
- Year
- 2004
- Shift
- Unknown
- Q Number
- Q65
- Type
- MCQ
- NCERT Ref
- Class 12 Physics Ch 9: Ray Optics
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