Explain the formation of a rainbow with the help of a diagram.

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Accepted Answer

A rainbow forms when sunlight is behind water droplets suspended in the air after rain. Each droplet acts like a tiny prism. Sunlight entering a spherical water droplet first refracts, splitting into its seven constituent colours. These separated colours then undergo total internal reflection at the far (inner) surface of the droplet. As they exit the droplet, they refract a second time, separating further. Red light, which is deviated the least, emerges to form the outer/upper part of the arc, while violet light, deviated the most, forms the inner/lower part.