Physics
Stars twinkle because

the intensity of light emitted by them changes with time.
the refractive index of the different layers of the earth's atmosphere ch
None of these
the distance of the stars from the earth changes with time.

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Physics
Rainbows are produced when sunlight :

Incident on raindrops hanging in the atmosphere is dispresed after suffering reflection.
Incident on rain drops hanging in the atmosphere is dispersed after suffering refraction
None of the given statements is correct.
Incident on rain drops hanging in the atmosphere is dispersed after suffering refraction and internal reflection.

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