question_answer

Direction for: In each of the following questions a statement of Assertion is given followed by a corresponding statement of Reason just below it. Of the statements mark the correct answer as

Assertion: In optical fibre, the diameter of core is kept small. Reason: 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 the reason is the correct explanation of assertion.

B) If both assertion and reason are true but the reason is not the correct explanation of the assertion.

C) If assertion is true statement but reason is false.

D) If both assertion and reason are false.

Correct Answer: A

Solution :

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. Hence, option (a) is true.