Practice portal › Ray Optics and Optical Instruments › Refraction and Total Internal Reflection
Asked in GSEB Board March 2020; GSEB Board July 2021 · Total internal reflection and optical fibres
Given: the core and the cladding of an optical fibre.
Idea: a fibre carries light by total internal reflection, which happens only when light goes from a denser medium into a rarer one and strikes the boundary beyond the critical angle.
The light travels inside the core, so the core must be the denser medium: its refractive index is higher than the cladding's.
The two indices are kept close together on purpose, so that the critical angle C = sin⁻¹((n_cladding)/(n_core)) is large and only rays nearly along the axis are trapped.
Every ray that enters within that cone then reflects along the fibre without loss at each bounce, however much the fibre is bent.
So the core's refractive index is higher than the cladding's.
Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.
Practise this with a timer