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1 PHYSICS MCQS

Rainbow is seen after rain because of hanging molecules of water which act as ?

  • Lens
  • Prism
  • Prism
  • Slabs
Correct Answer: B. Prism

Detailed Explanation

A rainbow is a meteorological phenomenon that occurs when sunlight interacts with suspended water droplets in the atmosphere, usually after rain. These water droplets serve as tiny prisms, bending and splitting sunlight into its constituent colors: red, orange, yellow, green, blue, indigo, and violet.


🔹 How Water Droplets Act as a Prism




  1. Refraction: Sunlight enters the water droplet and changes speed, bending slightly due to the difference in refractive index between air and water.




  2. Dispersion: The refracted light splits into different wavelengths (colors) because each color bends at a slightly different angle.




  3. Internal Reflection: Light reflects off the inner surface of the droplet.




  4. Refraction Again: Light exits the droplet and bends again, directing colors toward the observer’s eye.




🔹 Why a Rainbow Appears After Rain




  • After a rain shower, countless tiny droplets hang in the atmosphere.




  • Sunlight passing through these droplets creates multiple mini-prisms, each producing a spectrum of colors.




  • Combined, these spectra appear as a circular arc in the sky, commonly called a rainbow.




🔹 Key Points




  • Rainbows always appear opposite the Sun, with the observer’s back to the sunlight.




  • The primary rainbow is brighter and has red on the outer edge and violet on the inner edge.




  • Sometimes, a secondary rainbow appears outside the primary one with reversed colors due to double reflection inside droplets.




🔹 Misconceptions




  • It is not a mirror, lens, or slab**—though lenses can bend light, the rainbow specifically results from refraction, dispersion, and reflection in water droplets acting as prisms.






✅ Key Facts Recap




  • Rainbow formation = Sunlight + water droplets




  • Water droplets act as prisms




  • Involves refraction, dispersion, and reflection




  • Primary rainbow: Red outer, violet inner




👉 Correct Answer: Option 2 – Prism

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