Explain the formation of rainbow in the sky with the help of a diagram.
Explain the formation of rainbow in the sky with the help of a diagram.
A rainbow is a natural spectrum that appears in the sky after a rain shower. It is caused by the dispersion of sunlight by tiny water droplets present in the atmosphere. A rainbow is always formed in a direction opposite to that of the Sun.\n\nThe water droplets act like small prisms. The sunlight falling on a water droplet undergoes the following three processes:\n1. Refraction and Dispersion at the surface of the water droplet as light enters it.\n2. Internal reflection of the dispersed light from the inner surface of the droplet.\n3. Refraction of the dispersed light again as it emerges out of the droplet.\n\nDue to the dispersion of light and internal reflection, the different colours of sunlight reach the observer's eye at slightly different angles, producing a beautiful band of seven colours (VIBGYOR) in the sky - the rainbow.\n\n``diagram\n{\n "title": "Formation of Rainbow through a Water Droplet",\n "elements": [\n {"type": "circle", "cx": 320, "cy": 50, "r": 28, "fill": "yellow", "stroke": "orange", "label": "Sun"},\n {"type": "line", "from": [300, 75], "to": [200, 170], "color": "white", "label": "White sunlight"},\n {"type": "circle", "cx": 180, "cy": 200, "r": 35, "fill": "lightblue", "stroke": "blue", "label": "Water droplet"},\n {"type": "label", "x": 235, "y": 110, "text": "1. Refraction & Dispersion", "color": "red"},\n {"type": "line", "from": [180, 235], "to": [210, 225], "color": "violet", "label": ""},\n {"type": "label", "x": 230, "y": 215, "text": "2. Internal Reflection", "color": "darkgreen"},\n {"type": "line", "from": [210, 225], "to": [160, 250], "color": "red", "label": ""},\n {"type": "label", "x": 80, "y": 270, "text": "3. Refraction (emergence)", "color": "blue"},\n {"type": "line", "from": [160, 250], "to": [80, 330], "color": "red", "label": "Red - bends least"},\n {"type": "circle", "cx": 70, "cy": 350, "r": 12, "fill": "gray", "label": "Observer"},\n {"type": "label", "x": 60, "y": 400, "text": "Rainbow seen opposite to Sun", "style": "italic bold"}\n ]\n}\n``
Marking Scheme
- 11 mark: Correctly describing the three processes - refraction, internal reflection and refraction (or dispersion) - in a water droplet.
- 21 mark: Labelling the diagram clearly with sunlight, water droplet, internal reflection and observer, OR mentioning that a rainbow is formed in the direction opposite to the Sun.
Hint
A water droplet acts like a glass prism combined with a mirror. What three optical processes does a light ray undergo as it passes through such a droplet?
Quick Oral Answer
Q: Can a rainbow be formed on the Moon?\nA: No, because the Moon has no atmosphere and no water droplets to disperse sunlight. A rainbow requires both sunlight and water droplets (or other tiny droplets) suspended in the atmosphere.
Analysis & Explanation
A rainbow is essentially a result of three optical phenomena acting together: refraction, internal (total) reflection, and dispersion. The angle between the incoming sunlight and the direction of light emerging from the droplet is approximately for red and for violet. This difference of about is what causes the colour separation we see. Since the observer's eye must be aligned at a specific angle to the incoming sunlight, the rainbow is always seen in the direction opposite to the Sun. A second, fainter rainbow (with colours reversed) may sometimes appear due to two internal reflections inside the droplet.
Common Mistakes
- 1Saying that the rainbow is formed by reflection alone.
- 2Writing the colour order in reverse (ROYGBIV instead of VIBGYOR).
- 3Forgetting to mention that a rainbow is always formed in a direction opposite to the Sun.
- 4Confusing a rainbow (caused by water droplets) with a prism spectrum.
- 5Drawing a diagram without showing the path of light through the droplet.
Interesting Facts
A rainbow is not located at a fixed position in space - every observer sees a different rainbow, because each observer's eye is at a different angle relative to the Sun and droplets.
The primary rainbow has red on the outer edge and violet on the inner edge. A secondary rainbow (fainter, with reversed colours) may form due to two internal reflections inside the droplet.
You can also see a rainbow on a sunny day when you look at the sky through a waterfall or fountain, with the Sun behind you.
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2011?
This question carries 2 marks in the CBSE Class 10 Science 2011 examination.
Which chapter does this question come from in Science?
This question is from the chapter "The Human Eye and the Colourful World" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Atmospheric Phenomena - Rainbow" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2011 paper?
This is a Short Answer question from Section A in the CBSE Class 10 Science 2011 paper.