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

Options

A. If both the assertion and reason are true and reason explains the assertion.
B. If both the assertion and reason are true but reason does not explain the assertion.
C. If assertion is true but reason is false.
D. If assertion is false but reason is true.

Answer

A

Explanation

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 material. The core dimension of optical fibres is so small `(~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.