Chapter 6: Refraction of Light – Class 10 Science Notes

Explore the fascinating world of refraction of light with this detailed, easy-to-understand guide tailored for Maharashtra Board Class 10 Science. We’ll cover all key concepts, diagrams, formulas, examples, and practical applications—perfect for SSC exam preparation.

1. What is Refraction?

2. Laws of Refraction (Snell's Laws)

1. First law: The incident ray, refracted ray, and normal all lie in the same plane.
2. Second law: The ratio of the sine of the angle of incidence (i) to sine of the angle of refraction (r) is constant for two given media.
   i.e., sin(i)/sin(r) = constant = refractive index (n)

Medium Pair	Refractive Index (n)
Air → Water	≈ 1.33
Air → Glass	≈ 1.5

3. Refraction Through a Glass Prism

Light entering a prism is refracted twice—first at entry, then at exit—causing deviation. The amount of deviation depends on the angle of the prism and refractive index.

Formula: δ = (i + e) – A
Where δ = angle of deviation, i = angle of incidence, e = angle of emergence, A = prism angle.

4. Determining Refractive Index of a Prism

Using geometry and Snell’s law, refractive index can be calculated from:

5. Refraction Through Lenses (Introductory)

Converging and diverging lenses bend light differently, based on their shape and refractive index. The **Lens Maker’s Formula** relates focal length (f), refractive index (n), and curvature radii (R₁, R₂).

6. Dispersion of Light & Rainbow Formation

When white light refracts through a prism or water droplets, it splits into colors—a process called dispersion. Rainbows form when sunlight refracts, reflects, and disperses through raindrops.

7. Atmospheric Refraction

• Stars appear slightly shifted above their true position.
• Sunset appears below the horizon after it has set.
• Twinkling of stars is due to atmospheric refraction.

8. Solved Numerical Example

If a small angle prism has A = 30° and minimum deviation D = 10°, find n.

Solution: n = sin[(A + D)/2] / sin(A/2) = sin(20°) / sin(15°) ≈ 1.28

9. Diagrams to Practice Drawing

• Refraction at a plane surface
• Light passing through a prism
• Rainbow formation schematic

🔑 Summary – Key Takeaways

• Refraction bends light when it enters a different medium.
• Refractive index = sin(i)/sin(r) = c/v.
• Prism causes dispersion and deviates light.
• Atmospheric refraction causes natural optical effects.