Question

Optical fibre works on the principle of:

• A. Total internal reflection
• B. Refraction
• C. Interference
• D. Scattering

Hint:

Think about how light is trapped inside the denser core without ever crossing into the cladding.

Answer 1

The Correct Option is A

Step 1: An optical fibre is a thin, flexible strand of glass or plastic made of two layers, a central core with a higher refractive index, surrounded by an outer cladding with a lower refractive index.

Step 2: Light is sent into the fibre at one end so that it strikes the boundary between the core and the cladding at an angle greater than the critical angle for that pair of materials.

Step 3: When light hits a boundary from a denser, higher refractive index, medium to a rarer, lower refractive index, medium at an angle greater than the critical angle, none of the light escapes into the rarer medium, all of it reflects back into the denser medium. This is total internal reflection.

Step 4: Because this condition is maintained at every bounce along the length of the fibre, the light keeps reflecting internally again and again, travelling down the entire length of the fibre with almost no loss, even around gentle bends.

Step 5: This repeated bouncing by total internal reflection is exactly what carries light signals through an optical fibre over long distances, so the correct answer is option A.