Question

In optical fibre, the diameter of the core is kept small. This smaller diameter of the core ensures that the fibre should have incident angle more than the critical angle required for total internal reflection.

• A. If both assertion and reason are true and reason is the correct explanation of the assertion
• B. If both assertion and reason are true but reason is not the correct explanation of the assertion
• C. If assertion is true, but reason is false
• D. Both assertion and reason are false statements

Answer 1

Answer: (A)

If both assertion and reason are true and reason is the correct explanation of the assertion

Answer 2

In a point-to-point communication link using electrical signal, we use a conducting wire or a cable and the signal current is guided through the conductor cable wire. Light cannot pass through metal but can pass through a transparent glass, polymer or dielectric. Therefore, optical transmission line (called optical fibre) is made from any of these materials. The core dimension of optical fibres is so small $(\sim 10 \,\mu m )$ that the light entering will almost essentially be having incident angle more than the critical angle and will suffer total internal reflection at the core-cladding boundary. Such successive total reflections at opposite boundaries will confine the light to the core as shown in figure.