Discussion
Most useful physical property of fibers from forensic viewpoint is that many manufactured fibers exhibit :
Answer: A
Many manufactured fibres exhibit double refraction or birefringence.
When a synthetic fibre is drawn during manufacture, its polymer molecules line up along the fibre axis. Light polarised parallel to the axis then travels at a different speed from light polarised across it, so the fibre has two refractive indices. Their difference, the birefringence, is measured with a polarising microscope and is characteristic of the fibre type, distinguishing nylon, polyester, acrylic and others.
Colour, diameter and texture are useful for comparison, but they can be varied freely by the manufacturer and are not a property of the polymer itself, so they do not identify the fibre type as birefringence does.
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