Light – Reflection and Refraction – CBSE Class 10 Revision Notes

Light – Reflection and Refraction – CBSE Class 10 Revision Notes

Chapter 6: Light – Reflection and Refraction – CBSE Class 10 Revision Notes

Welcome to your ultimate Class 10 Science revision notes for Chapter 6: Light – Reflection and Refraction. These exam-focused, SEO-friendly notes are crafted in simple language to help you score high in CBSE Physics. Whether you’re revising before the exam or learning for the first time, these NCERT chapter 6 quick summary notes cover all important points, definitions, laws, and applications in a clear, concise manner.

What Is Light?

Light is a form of energy that makes objects visible to our eyes. In Class 10 Physics, you’ll learn that light travels in a straight line in a homogeneous medium, known as rectilinear propagation. It behaves both as a wave and as particles called photons, demonstrating its wave-particle duality. Understanding this duality is essential for grasping phenomena like interference and diffraction in higher classes, but for Chapter 6, focus on its straight-line motion, reflection, and refraction.

Laws of Reflection

Reflection occurs when light bounces off a surface. There are two fundamental laws:

1. Angle of Incidence = Angle of Reflection: If a light ray strikes a mirror at an angle i to the normal, it leaves at the same angle r on the other side of the normal.

2. Incident Ray, Reflected Ray, and Normal Are Coplanar: All three lie in the same plane perpendicular to the mirror surface. These laws form the backbone of mirror-related problems in your exam.

Types of Reflection

Reflection can be regular (specular) or diffuse:

Regular Reflection: Occurs on a smooth, polished surface (like a plane mirror). Reflected rays remain parallel, producing a clear image.

Diffuse Reflection: Occurs on rough surfaces. Reflected rays scatter in many directions, so no clear image forms. Both types are frequently tested in short-answer questions.

Image Formation by Plane Mirrors

Plane mirrors produce images with these key characteristics:

  • Virtual: Cannot be caught on a screen.
  • Erect: Upright relative to the object.
  • Laterally Inverted: Left and right are swapped.
  • Same Size: Image distance equals object distance.

Memorize the mirror formula (image distance = object distance) and the concept of lateral inversion for drawing ray diagrams accurately.

Refraction of Light

Refraction is the bending of light as it passes from one medium to another with a different optical density. Key points to remember:

Refractive Index (n): Ratio of the speed of light in vacuum to that in the medium, n = c/v.

Snell’s Law: n₁·sin i = n₂·sin r, where i is the angle of incidence in medium 1 and r is the angle of refraction in medium 2. This law is central to solving numerical problems in your exam.

Refraction Through a Glass Slab

When light enters and exits a glass slab of parallel faces:

  • It deviates from its original path but emerges parallel to the incident ray.
  • Lateral Shift: The perpendicular distance between the incident and emergent rays. Depends on thickness, refractive index, and angle of incidence.

Practice drawing ray diagrams and calculating lateral shifts to score well in long-answer questions.

Total Internal Reflection (TIR)

TIR occurs when light tries to travel from a denser medium to a rarer medium at an angle greater than the critical angle (C). Conditions:

1. Light travels from denser to rarer medium (e.g., water to air).
2. Angle of incidence > Critical angle.

Applications of TIR include optical fibers, prisms in periscopes and binoculars, and medical endoscopes. Be prepared to explain why optical fibers are ideal for high-speed data transmission in your exam.

Key Formulae and Derivations

Memorize these formulae and derivations, as they are frequently asked:

  • Refractive Index: n = sin i / sin r
  • Critical Angle: sin C = 1 / n (for denser to rarer medium)
  • Lateral Shift (d): d = t·sin(i – r) / cos r, where t is slab thickness.

Understanding derivations helps you handle application-based questions.

Exam-Focused Revision Tips

Follow these quick tips to maximize your score:

  • Draw Clear Ray Diagrams: Label all angles and normals.
  • Highlight Laws and Definitions: Use your own words to remember easily.
  • Practice Numerical Problems: At least 5–10 problems on refractive index and lateral shift.
  • Revise Applications: Be able to explain fiber optics and periscope function in 2–3 lines.

Common Examination Questions

Be ready for these question types:

  • Short Answer (2–3 marks): Define refraction, state laws of reflection, label ray diagrams.
  • Long Answer (5 marks): Derive refractive index formula, explain total internal reflection with diagram.
  • Numerical (2–3 marks): Calculate refractive index, critical angle, lateral shift.
  • Application-Based: Explain how optical fibers work in telecommunications.

Real‑Life Applications

The concepts of reflection and refraction have everyday uses:

  • Mirrors: Used in shaving mirrors, rear‑view mirrors, and telescopes.
  • Lenses and Prisms: Used in glasses, cameras, and binoculars.
  • Optical Fibers: Enable fast internet, medical imaging, and secure data transfer.

Relating theory to real life helps in descriptive answers and interviews.

Final Quick Checklist

Before the exam, ensure you have:

  • Revised all laws (reflection, refraction).
  • Practiced ray diagrams for mirrors and slabs.
  • Memorized formulae and derivations.
  • Understood applications of total internal reflection.
  • Attempted sample papers and NCERT exemplar questions.

Disclaimer: These notes are meant for revision and exam preparation. For comprehensive understanding, refer to the NCERT textbook and consult your teacher for any doubts.

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