Explaining Raised Letters Under Glass Slab

When a thick glass slab is placed over printed matter, the letters appear raised due to the phenomenon of refraction of light. Refraction is the bending of light as it passes from one medium to another where its speed changes.

Understanding Refraction

• Light travels from the ink on the paper, through the glass slab, and then into the air before reaching the observer's eye.
• As light rays emerge from the glass (denser medium) into the air (rarer medium), they bend away from the normal.
• This bending changes the apparent position of the letters, making them seem closer to the surface and thus appearing raised.

Analyzing Other Options

• A. Scattering of light: This involves light deviating in multiple directions, not causing a specific raised appearance.
• C. Total internal reflection: This occurs when light travelling from a denser to a rarer medium hits the boundary at an angle greater than the critical angle, reflecting back into the denser medium. This is not the primary reason for the raised appearance here.
• D. Polarization of light: This refers to the orientation of the light wave's oscillations and does not explain the perceived change in position of the letters.

Therefore, the apparent raising of the letters is solely due to the bending of light rays, which is refraction.