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Refraction of Light at spherical surfaces: Lenses — Syllabus

ICSE · Class 12 · Physics

What Refraction of Light at spherical surfaces: Lenses covers in ICSE Class 12 Physics: 4 topics, for the 2026-27 session.

39 questions32 flashcards8 formulas & key relations5 concepts

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4 Topics · ICSE Class 12 Physics · 2026-27

Topics in Refraction of Light at spherical surfaces: Lenses

1

1. Sign Convention and Basic Geometry

  • The optical centre of the lens is taken as origin and principal axis of the lens as X-axis.
  • Distances measured to the right of the optical centre are positive and distances measured to the left are negative.
  • Distances measured upward from principal axis are positive and those measured downward are negative.
2

2. Refraction at a Spherical Surface

  • A concave spherical refracting surface separating a rarer medium from a denser medium forms only a virtual image in the first medium.
  • A convex spherical refracting surface separating a rarer medium from a denser medium forms a real image on the far side.
  • The same final formula applies to both concave and convex surfaces when the object lies in the rarer medium.
3

3. Foci of a Spherical Refracting Surface

  • First focus is the point from which rays start, or towards which rays appear to go, so that after refraction they emerge parallel to the principal axis.
  • Second focus or principal focus is the point where axial parallel rays converge, or from which they appear to diverge, after refraction.
  • The focus in a convex lens is real while in a concave lens it is virtual.
4

4. Lenses, Optical Centre, and Types

  • A lens is a transparent medium bounded by two curved surfaces or one curved and one plane surface.
  • Most lens surfaces are spherical.
  • A convex lens is thicker in the middle and thinner at the edges.

Key Concepts

Central concept: Refraction of light through spherical surfaces and thin lenses

Coordinate geometry sign conventionRefraction at spherical surfacesLens as an optical deviceOptical centre and foci of a lensLens maker's formulaLens formula and magnificationPower of a lensCombination of thin lenses

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Frequently Asked Questions

What are the important topics in Refraction of Light at spherical surfaces: Lenses for ICSE Class 12 Physics?
Key topics in Refraction of Light at spherical surfaces: Lenses include Sign Convention and Basic Geometry, Refraction at a Spherical Surface, Foci of a Spherical Refracting Surface, Lenses, Optical Centre, and Types. Study these first, then practise questions on each for the ICSE Class 12 board exam.
How should I revise Refraction of Light at spherical surfaces: Lenses for the ICSE Class 12 board exam?
Learn the core ideas first, then work through the 39 practice questions on Refraction of Light at spherical surfaces: Lenses. 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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