Question

The most fundamental physical principle that allows light to be transmitted along the optical fiber without significant loss :

• A. The photoelectric effect
• B. Total internal reflection
• C. Bragg's law
• D. The Seebeck effect

Hint:

Optical fiber works because: \[ n_{\text{core}} > n_{\text{cladding}} \] which enables repeated total internal reflection of light rays.

Answer 1

The Correct Option is B

Concept: Optical fiber communication works on the principle of: \[ \text{Total Internal Reflection (TIR)} \] Light entering the fiber core repeatedly reflects from the core-cladding boundary and remains confined inside the fiber.

Step 1: Understand optical fiber structure. An optical fiber mainly consists of:
• Core
• Cladding The refractive index satisfies: \[ n_{\text{core}} > n_{\text{cladding}} \] This condition is essential for total internal reflection.

Step 2: Explain total internal reflection. When light travels from: \[ \text{Denser medium} \rightarrow \text{Rarer medium} \] and the angle of incidence exceeds the critical angle: \[ \theta_i > \theta_c \] the light is completely reflected back into the denser medium. This phenomenon is called: \[ \text{Total Internal Reflection} \]

Step 3: Apply TIR to optical fibers. Inside optical fiber:
• Light travels through the core.
• At the core-cladding boundary, repeated total internal reflection occurs. As a result:
• Light remains trapped inside the fiber.
• Signal transmission occurs with very small loss.

Step 4: Analyze other options. Option A: Photoelectric effect This refers to emission of electrons from metal surfaces due to incident light. Not related to fiber propagation. Option C: Bragg's law Bragg's law is associated with: \[ \text{X-ray diffraction in crystals} \] Not related to optical fiber transmission. Option D: Seebeck effect Seebeck effect is: \[ \text{Generation of emf due to temperature difference} \] Not related to optical communication.

Step 5: Write final answer. Therefore the correct answer is: \[ \boxed{\text{Total Internal Reflection}} \]