✓ Board-verified
Physics · 2026 · 3 marks
CBSE 2026 · Region 1 · Set 3 · Q28
(a) Why does one prefer to view the image formed at infinity than that formed at near point in microscope/telescope? (b) Consider lenses L_1, L_2 and…
(a)
Why does one prefer to view the image formed at infinity than that formed at near point in microscope/telescope ?
(b)
Consider lenses $\displaystyle \mathrm{L}_{1}, \mathrm{~L}_{2}$ and $\displaystyle \mathrm{L}_{3}$ as specified in the following table. Which of them will you select as objective and eyepiece for constructing best possible (i) telescope (ii) compound microscope ? Give reason for your answer.
$\displaystyle 3$
| Lens | $\displaystyle \mathrm{L}_{1}$ | $\displaystyle \mathrm{L}_{2}$ | $\displaystyle \mathrm{L}_{3}$ |
| Power | $\displaystyle 6$ D | $\displaystyle 3$ D | $\displaystyle 10$ D |
| Aperture | $\displaystyle 1$ cm | $\displaystyle 8$ cm | $\displaystyle 1$ cm |
Marking-scheme solution
(a)
In the case of normal adjustment, the eye muscles remain relaxed while they are strained in the case when image is formed at near point while viewing the object, hence it is preferred.
(b)
For Telescope
Lense $\displaystyle \mathrm{L}_{2}$ is suitable as objective Lens
Lense $\displaystyle \mathrm{L}_{3}$ is suitable as eyepiece
For Compound microscope
Lense $\displaystyle \mathrm{L}_{3}$ is suitable as objective lens
Lense $\displaystyle \mathrm{L}_{1}$ is suitable as eyepiece
Reason
For telescope, objective lens should have large aperture and large focal length
For microscope, objective and eye lens should have moderate aperture but the objective should have large power.
All Ray Optics and Optical Instruments questions2026 question paperNCERT solutions: Ray Optics and Optical InstrumentsPractice Ray Optics and Optical Instruments →
More from Ray Optics and Optical Instruments
- A small bulb is placed at the bottom of a tank, containing a transparent liquid of refractive index √2, to a depth of 1 m. Calculate the area of the…2026
- Assertion: A convex lens, when immersed in a liquid, disappears. Reason ( R ): The refractive indices of material of the lens and the liquid are…2024
- A right angled isosceles glass prism ABC is kept in contact with an equilateral triangular prism DBC as shown in the figure. Both prisms are made of…2025
- A convex lens (n = 1.52) has a focal length of 15.0 cm in air. Find its focal length when it is immersed in liquid of refractive index 1.65. What…2024
- (i) Draw a labelled ray diagram showing the formation of the image at infinity by an astronomical telescope. (ii) A telescope consists of an…2022
- Two convex lenses A and B, each of focal length 10.0 cm, are mounted on an optical bench at 50.0 cm and 70.0 cm respectively. An object is mounted at…2025
- A right-angled prism ABC (refractive index √2 ) is kept on a plane mirror as shown in the figure. A ray of light is incident normally on the face AC.…2025
- A ray of light is incident on a glass prism of refractive index μ and refracting angle A. If it just suffers total internal reflection at the other…2023
CBSE Class 12 Physics past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.