Light weight bullet proof helmets and jackets use which of the following fibres for their production ?

Question

UnlockIAS · Accepted Answer

Correct — A, Kevlar. Kevlar is a para-aramid — chemically poly-paraphenylene terephthalamide — a strong, heat-resistant synthetic fibre developed by Stephanie Kwolek at DuPont in 1965 and related to other aramids such as Nomex and Technora. Its usefulness in armour comes from its molecular architecture. The polymer chains are rigid rods rather than the flexible coils of an ordinary plastic, and when spun they line up almost perfectly along the fibre axis, held side by side by dense hydrogen bonding. The result is a fibre roughly five times stronger than steel on a weight-for-weight basis, which is exactly the property the stem's words 'light weight' are pointing at. A bullet striking a woven Kevlar panel is not stopped by hardness but by energy absorption: the fibres at the point of impact stretch and pull on the fibres woven across them, so the projectile's kinetic energy is spread through the whole fabric and dissipated over many layers instead of punching through one. That is also why soft armour is built from many layers of loosely woven cloth rather than from one stiff sheet. Since option (a) names the fibre correctly, the escape option has nothing left to cover. The other two named fibres are real and important, but neither has the tenacity to do this job at a weight a soldier or a police officer can carry all day.

Why the other options are wrong — (b) Terylene is a polyester — polyethylene terephthalate — the fibre of ordinary shirting, curtains and blended suiting, and the same polymer family as the plastic drinks bottle. It is durable, crease-resistant and cheap, and it is nowhere near the tenacity or energy absorption needed to stop a projectile. It is on the list because it is the synthetic fibre an Indian candidate is likeliest to have heard of by trade name.  (c) The strongest wrong answer, and one with real history behind it: nylon, a polyamide, was tough enough that wartime flak jackets were made from it, and it is still used in ballistic liners and in the backing of composite armour. But modern light armour moved to aramids and to ultra-high-molecular-weight polyethylene precisely because nylon cannot deliver the same stopping power without becoming heavy — and the stem's qualifier 'light weight' is what rules it out.  (d) This escape needs all three named fibres to fail, and the first one is the standard answer. The only reading that could support it is that modern armour is not made of Kevlar alone — ultra-high-molecular-weight polyethylene and ceramic plates share the field — but naming one correct material is not a claim that it is the only one.

Concept: Synthetic fibres are long-chain polymers spun into filaments, and their properties follow from what the chains are made of and how well they line up. Nylon, invented at DuPont in the 1930s, is a polyamide: chains joined by amide links, tough and elastic, the fibre of parachutes, ropes and stockings. Polyester, marketed as Terylene, joins its units by ester links and gives a stiff, hydrophobic, crease-resistant fibre that dominates ordinary clothing. Aramids are aromatic polyamides — the amide links now join benzene rings rather than flexible carbon chains — and that aromatic backbone is what makes them rigid, heat-resistant and enormously strong along the fibre. Kevlar's rods pack in sheets and are exceptionally hard to pull apart; its cousin Nomex is arranged differently and is used for flame-resistant clothing rather than ballistic protection. The same logic of chain alignment explains ultra-high-molecular-weight polyethylene, the other modern armour fibre: an ordinary plastic becomes extraordinary when its very long chains are drawn into near-perfect parallel order. Body armour in practice combines these fibres with ceramic or steel plates, the fabric absorbing energy and the plate breaking up the projectile.

State PCS 2025 Q86 — Science & Technology PYQ with Answer

State PCS 2025 Q86 — Science & Technology PYQ with Answer