Question:medium

A rectangular glass block of thickness 10 cm and refractive index 1.5 is placed over a small coin. A beaker is filled with water of refractive index 4/3 to a height of 10 cm and placed over the glass block. The apparent depth of coin when viewed at near normal incidence is:

Show Hint

Apparent depth is additive; calculate the apparent depth for each layer independently and sum them up.
Updated On: Jun 9, 2026
  • \( 3.3 \text{ cm} \)
  • \( 5.8 \text{ cm} \)
  • \( 12.0 \text{ cm} \)
  • \( 14.2 \text{ cm} \)
Show Solution

The Correct Option is D

Solution and Explanation

Step 1: Idea of apparent depth.
Looking straight down through a transparent slab, an object seems raised. Each slab gives an apparent depth $d_{\text{app}} = \dfrac{d_{\text{real}}}{\mu}$, and with two stacked media the apparent depths simply add.
Step 2: Layers present.
The coin sits below $10\,\text{cm}$ of glass ($\mu = 1.5$) which is itself below $10\,\text{cm}$ of water ($\mu = 4/3$).
Step 3: Apparent depth through the glass.
\[ d_1 = \frac{10}{1.5} = \frac{10}{3/2} = \frac{20}{3} \approx 6.67\,\text{cm}. \]
Step 4: Apparent depth through the water.
\[ d_2 = \frac{10}{4/3} = \frac{30}{4} = 7.5\,\text{cm}. \]
Step 5: Add the two contributions.
\[ d_{\text{total}} = d_1 + d_2 = 6.67 + 7.5 = 14.17\,\text{cm}. \]
Step 6: Round to the option.
The apparent depth of the coin is about $14.2\,\text{cm}$.
\[ \boxed{14.2\ \text{cm}} \]
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