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Syllabus

Optical Instruments — Syllabus

NIOS · Class 12 · Physics

What Optical Instruments covers in NIOS Class 12 Physics: 4 topics, for the 2026-27 session. Part of the NIOS Class 12 Physics syllabus.

43 questions40 flashcards14 formulas & key relations5 concepts

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A ray diagram illustrating the working of a simple microscope (converging lens) to produce a magnified, virtual, and erect image when the object is placed between the optical center and the focal poin
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4 Topics · NIOS Class 12 Physics · 2026-27

Topics in Optical Instruments

1

Key Definitions and Basic Concepts

  • Near Point: The closest distance at which the eye can see an object clearly. For a normal human eye, it is approximately 25 cm. This distance varies with age — children can have a near point as close
  • Least Distance of Distinct Vision (D): The minimum distance (25 cm for a normal eye) at which the eye sees an object clearly without any strain. Represented by D = 25 cm.
  • Far Point: The farthest point up to which the eye can see clearly without strain. For a normal eye, this is at infinity.
2

Simple Microscope (Magnifying Glass)

  • A simple microscope is a single convex lens of short focal length used to see magnified images of small nearby objects.
  • The object is placed between F (focus) and O (optical centre) of the convex lens. The image formed is virtual, erect, and magnified on the same side as the object.
  • The eye is placed close to the lens and the object distance is adjusted until the image appears at the least distance of distinct vision (D = 25 cm).
3

Compound Microscope

  • A compound microscope uses two convex lenses — the Objective (faces the object, short focal length, small aperture) and the Eyepiece (faces the eye, short focal length, larger aperture).
  • The objective has a SHORTER focal length than the eyepiece. Both lenses have short focal lengths.
  • Working: Object AB is placed just beyond 2F of the objective. The objective forms a real, inverted, magnified intermediate image A'B' beyond 2F on the other side.
4

Refracting Telescope (Astronomical Telescope)

  • A refracting telescope uses two convex lenses — the Objective (large focal length, large aperture) and the Eyepiece (short focal length, small aperture).
  • Unlike microscope, the telescope objective has a LARGE focal length. This is the key difference.
  • Working: Parallel rays from a distant object fall on the objective and form a real, inverted, diminished image at its focal plane (since object is at infinity).

Key Concepts

Central concept: Optical Instruments use lenses and mirrors to enhance our ability to see objects that are too small or too distant for the unaided eye

Simple MicroscopeCompound MicroscopeRefracting TelescopeReflecting TelescopeKey DefinitionsResolving Power

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Frequently Asked Questions

What are the important topics in Optical Instruments for NIOS Class 12 Physics?
Key topics in Optical Instruments include Key Definitions and Basic Concepts, Simple Microscope (Magnifying Glass), Compound Microscope, Refracting Telescope (Astronomical Telescope). Study these first, then practise questions on each for the NIOS Class 12 board exam.
How should I revise Optical Instruments for the NIOS Class 12 board exam?
Learn the core ideas first, then work through the 43 practice questions on Optical Instruments. Revise definitions regularly and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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