Light — Reflection and Refraction (Class 10)
About 6 min · Science · English
Time worked out from the lesson's 395 words at 150 words a minute, plus a minute for each question.
Light — Reflection and Refraction is part of the NSO Class 10 Science syllabus. It combines conceptual understanding with numerical problem-solving, covering both mirrors and lenses. Students must master sign conventions, formula application, and the behavior of light at boundaries between different media.
Key ideas
- Laws of Reflection: The incident ray, reflected ray, and normal all lie in the same plane. The angle of incidence equals the angle of reflection (∠i = ∠r).
- Spherical Mirrors: Concave mirrors converge light (can form real or virtual images), while convex mirrors diverge light (always form virtual, diminished, erect images). The principal focus of a concave mirror is real; for a convex mirror, it is virtual.
- Refraction: When light travels from one transparent medium to another, it changes speed and bends at the boundary. Light bends toward the normal when entering a denser medium and away when entering a rarer medium.
- Refractive Index: The refractive index n of a medium is the ratio of the speed of light in vacuum to the speed of light in that medium. n = c/v. Higher refractive index means light travels slower in that medium.
- Snell's Law: At the interface of two media, n₁ sin i = n₂ sin r, where n₁ and n₂ are refractive indices and i, r are angles of incidence and refraction.
Quick reference
- Concave mirror: f negative, converges light, real/virtual images possible.
- Convex mirror: f positive (by magnitude convention), diverges light, always virtual/erect/diminished image.
- Convex lens: f positive, converges light, real/virtual images possible.
- Concave lens: f negative, diverges light, always virtual/erect/diminished image.
- Sign rule: Object distance u always negative; v negative = real image (mirror)/virtual (lens); v positive = virtual (mirror)/real (lens).
Check yourself: 3 questions
1. A ray of light travels from air into water. The refractive index of water is 1.33. If the speed of light in air is 3 × 10⁸ m/s, what is the speed of light in water?
2. An object is placed 15 cm in front of a concave mirror of focal length 10 cm. What is the image distance from the mirror?
3. A convex lens of focal length 20 cm forms an image at the same distance as the object is placed from the lens. What is the magnification produced by the lens?
This lesson is cut from the topic's note, not rewritten. Fact-checked on 21 Oct 2026: an AI-assisted check of this note against cited sources; the errors it found were corrected that day. Some errors may remain. The questions are from Shishya's validated question bank.
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