When a thick glass slab is placed over printed matter, they appear to be __________ and this is due to _______

Question

When a thick glass slab is placed over printed matter, they appear to be __________ and this is due to __________ of light.

Examoogle · Accepted Answer

The correct answer is Option C: raised; refraction. When a thick glass slab is placed over printed matter, the letters appear to be raised (closer to the top surface than they actually are). This phenomenon occurs due to the refraction of light as it travels from a denser medium (glass) to a rarer medium (air).

Step-by-Step Solution & Concepts:
When a thick glass slab is placed over printed matter, the letters appear to be raised (closer to the top surface than they actually are). This phenomenon occurs due to the refraction of light as it travels from a denser medium (glass) to a rarer medium (air).

Working Principle: Light rays originating from the printed matter pass from glass (denser medium, refractive index $n_2 > 1$) into air (rarer medium, refractive index $n_1 = 1$). According to Snell's Law, when light travels from a denser to a rarer medium, it bends away from the normal. When these refracted rays are extended backward, they intersect at a point closer to the observer than the actual position of the print, making the letters appear raised.

Key Formulas: $	ext{Apparent Depth} = \frac{	ext{Real Depth}}{n}$ — relationship between real and apparent depth; $	ext{Shift } (d) = t \left(1 - \frac{1}{n}ight)$ — formula for lateral or vertical apparent shift through a slab of thickness $t$

Key Points: When viewing through a medium of higher refractive index, objects appear closer (raised).; The phenomenon is governed by Snell's Law of Refraction.; The shift is directly proportional to the thickness of the glass slab ($t$) and depends on its refractive index ($n$).; Total internal reflection or lateral displacement may also occur depending on the angle of incidence.

Advantages: Demonstrates fundamental wave optics and refraction laws in classrooms.; Used in optical instruments like microscopes to calibrate focusing depths.

Disadvantages: Causes distortion and parallax errors if viewed at oblique angles.

Applications: Apparent shallow depth of swimming pools.; Bending of a pencil dipped obliquely in water.; Twinkling of stars and sunrise/sunset atmospheric refraction.

Additional Info: Refractive index of standard crown glass is approximately $1.5$.. Option A/B are incorrect because the phenomenon is refraction, not reflection, and the print appears raised, not lowered.

Answer: C is correct — raised; refraction

Exam Tip: Always remember: denser to rarer medium bends light AWAY from the normal, making submerged or covered objects appear closer/raised to the observer.

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