In an optical fibre

Options

A. Core region is transparent, cladding is opaque
B. Core region is opaque, cladding is transparent
C. Both core and cladding regions are transperent
D. Both core and cladding regions are opaque

Answer

To solve the question regarding the conditions in an optical fiber, we will analyze the properties of the core and cladding materials in relation to light transmission.

### Step-by-Step Solution:

1. **Understanding Optical Fiber Structure**:
- An optical fiber consists of a core and a cladding. The core is the central part through which light travels, while the cladding surrounds the core.

2. **Refractive Indices**:
- Let’s denote the refractive index of the core as \( N_1 \) and that of the cladding as \( N_2 \). For total internal reflection to occur, the refractive index of the core must be greater than that of the cladding, i.e., \( N_1 > N_2 \).

3. **Condition for Total Internal Reflection**:
- Total internal reflection occurs when light travels from a medium with a higher refractive index (the core) to a medium with a lower refractive index (the cladding). This is essential for the light to be confined within the core.

4. **Transparency Requirement**:
- For the optical fiber to function effectively, both the core and the cladding must be transparent to the light being transmitted. If either the core or the cladding is not transparent, the light will not propagate correctly, leading to losses.

5. **Conclusion**:
- Therefore, in an optical fiber, both the core and the cladding must be transparent. The core has a higher refractive index (N1) and the cladding has a lower refractive index (N2), which allows for total internal reflection to occur.

### Final Answer:
In an optical fiber, both the core and the cladding are transparent.

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