Observation

This question was clearly unpopular but it aimed at directing the thinking of candidates to materials used in making optic fibres. In response to the question, glass and silica were commonly given as two out of the three materials required. Polycarbonate, sapphire, eflon sheets were hardly mentioned but correct. Performance was fair.

The expected answer is

Materials for making optical fibre
-   Glass (in very fine strands)
-   Polycarbonate
-   Teflon sheath
-   Silica