Glass MCQ with answer and solution

Concept

Atomic structure and brittleness of glass

Formula

NONE

Step-by-step solution

1. Glass is an amorphous solid consisting of an irregular silicate network without crystal grains or mobile dislocations. 2. Under applied tensile loading, the absence of dislocation movement prevents any plastic yield or blunting of stress concentrations at surface micro-flaws. 3. Once the local Griffith fracture stress is reached, cracks propagate instantaneously across the section. 4. Hence, its brittleness is primarily due to its amorphous structure with no plastic deformation. Answer: B

Explanation

Glass has an amorphous non-crystalline structure without dislocation glide mechanisms, which prevents plastic yielding prior to fracture. When tensile stress reaches the critical threshold at micro-flaws, cracks propagate spontaneously without energy absorption. This complete lack of plastic deformation makes glass inherently brittle.

Why the other options are wrong

A) Glass has very low practical tensile strength because surface micro-cracks concentrate stress. C) Low thermal expansion improves thermal shock resistance, not mechanical ductility. D) Density does not dictate whether failure occurs in a brittle or ductile mode.

Shortcut

Amorphous network + zero dislocation movement = zero plastic deformation and extreme brittleness.

Common mistake

Attributing brittleness to high tensile strength rather than the material's inability to deform plastically.