Question

Assertion (A): Propagation of light through an optical fibre is due to total internal reflection taking place at the core-cladding interface.
Reason (R) : Refractive index of the material of the core of the optical fibre is greater than that of air.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A)
• B. Both (A) and (R) are true but (R) is not the correct explanation of (A)
• C. (A) is true and (R) is false
• D. (A) is false and (R) is true

Answer 1

Answer: (B)

Both (A) and (R) are true but (R) is not the correct explanation of (A)

Propagation of light through an optical fibre is due to total internal reflection taking place at the interface of cable and air. In this case, the refractive index of cable is such that light always has total internal reflection. Refractive index of the material of the cable of the optical fibre is greater than that of air.