Science (086) — CBSE Class 10 board question

Rainbow: A rainbow is a natural spectrum of light appearing in the sky after a rain shower. It is caused by dispersion of sunlight by tiny water droplets in the atmosphere. The water droplets act like small prisms — they refract and disperse sunlight, reflect it internally, and refract it again on exit. It is always formed in the direction opposite to the Sun.

Diagram:

```
Sunlight
│
▼
┌─────────┐
│ Water │ ← Refraction + Dispersion
│ Droplet │ ← Internal Reflection
└─────────┘
│
▼
V I B G Y O R → Observer's Eye
(Violet bends most, Red bends least)
```

Labels: Sunlight (incident), Water droplet, Internal reflection, Dispersed colours (VIBGYOR), Observer's eye.

Source: Chapter 10, Section 10.4 (Dispersion of White Light by a Glass Prism)

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• Definition (1 mark): Mention natural spectrum, rain shower, dispersion by water droplets.
• Mechanism (1 mark): Three steps — refraction + dispersion → internal reflection → refraction again on exit. Also note it forms opposite to the Sun.
• Diagram (1 mark): Show sunlight entering a circular droplet, internal reflection inside, colours emerging with VIBGYOR labelled. Violet at top (bends most), Red at bottom (bends least) in the actual rainbow arc.
• Examiners look for the word dispersion, internal reflection, and a neat labelled diagram. Don't skip any of the three optical steps.