(i) State the principle on which the working of an optical fiber is based.
(ii) What are the necessary conditions for this phenomenon to occur ?

Explanation

**Step-by-Step Solution:**

(i) The principle on which the working of an optical fiber is based is **total internal reflection**. This phenomenon occurs when a light ray traveling in a denser medium hits the boundary of a rarer medium at an angle greater than the critical angle, causing the light to be completely reflected back into the denser medium.

(ii) The necessary conditions for total internal reflection to occur are:

1. **The light ray must travel from a denser medium to a rarer medium.** This means that the optical fiber must have a core made of a material with a higher refractive index compared to the surrounding cladding.

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