Question

Explain how an optical fibre works. Why does the fibre still work when it is bent?

Short answer

When the fibre is bent, the${\theta }_j$angle exceeds the critical angle, preventing light from leaving the core.

Step-by-step solution

Definition of optical fibre.

An optical fibre is a transparent, flexible fibre manufactured by pulling glass or plastic to a diameter slightly larger than a human hair.

The working of optical fibre.

The light from an optical fibre strikes the core's wall at an angle of incidence called ${\theta }_j$. A portion of the light may be reflected inside the core, while the remainder may be transmitted at the refraction angle ${\theta }_r$.The Snell's law is:

${\mathrm{n}}_1·\sin {\theta }_j={\mathrm{n}}_2·\sin {\theta }_r$

All light is reflected if the incidence angle is larger than the critical angle for complete reflection.

The reason for working of optical fibre when it is bent.

When the fibre is bent, the${\theta }_i$will still exceed the critical angle, preventing light from leaving the core.