A plane glass slab is placed over various coloured letters. The letter which appears to be raised the least is

Options

A. violet
B. yellow
C. red
D. green

Explanation

To solve the problem of which colored letter appears to be raised the least when viewed through a plane glass slab, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Apparent Depth**:
- When light passes from one medium to another (in this case, from air to glass), it bends due to refraction. This bending causes objects viewed through the glass to appear at a different depth than they actually are.

2. **Identify the Relationship Between Real Depth and Apparent Depth**:
- The relationship between the real depth (H) and the apparent depth (h) is given by the formula:
\[ h = \frac{H}{\mu} \]
- Here, \( \mu \) is the refractive index of the medium (glass in this case). The apparent depth decreases as the refractive index increases.

3. **Determine the Effect of Refractive Index on Apparent Depth**:
- Since we want the letter to appear raised the least, we need to maximize the apparent depth (h). From the formula, this means we need to minimize the refractive index (μ).

4. **Compare the Refractive Indices of Different Colors**:
- Different colors of light have different refractive indices when passing through glass. Generally, red light has the lowest refractive index among the visible spectrum.
- Therefore, if we have various colored letters, the refractive indices can be arranged as follows (from lowest to highest):
- Red < Orange < Yellow < Green < Blue < Indigo < Violet

5. **Conclusion**:
- Since red light has the lowest refractive index, the apparent depth for the red letter will be the highest. Thus, the red letter will appear to be raised the least when viewed through the glass slab.

### Final Answer:
The letter which appears to be raised the least is the **red colored letter**.

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