Question

Transparency of glass is due to

• A. absence of grain boundaries
• B. presence of free electrons
• C. metallic bonding
• D. lack of scattering centres

Hint:

While the "absence of grain boundaries" is a prerequisite, the fundamental optical explanation for transparency is the "lack of scattering centers" of size comparable to visible light wavelengths.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks for the physical reason behind the optical transparency of glass.

Step 2: Key Formula or Approach:
Light passing through a material can be absorbed, reflected, or scattered. For a material to be highly transparent, light waves must pass through it with minimal scattering and absorption.

Step 3: Detailed Explanation:

• Glass is an amorphous solid with a homogeneous, non-crystalline structure.

• In crystalline materials, grain boundaries, phase boundaries, and microscopic pores act as defects that reflect and scatter light in different directions, making the material translucent or opaque.

• Because glass is amorphous, it lacks grain boundaries and has a highly uniform atomic structure on a scale comparable to the wavelength of visible light.

• This uniform structure means there are no localized changes in refractive index or physical interfaces to act as scattering centers.

• Furthermore, because glass has a wide electronic band gap, visible light photons do not have enough energy to excite electrons, preventing absorption.

• With both scattering and absorption suppressed, light passes through glass without being disrupted, resulting in its optical transparency.

Step 4: Final Answer:
The transparency of glass is due to the lack of scattering centers.