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Date November 2017 Marks available 3 Reference code 17N.3.HL.TZ0.15
Level Higher level Paper Paper 3 Time zone Time zone 0
Command term Calculate Question number 15 Adapted from N/A

Question

Some optic fibres consist of a core surrounded by cladding as shown in the diagram.

Calculate the maximum angle β for light to travel through the fibre.

Refractive index of core       = 1.50
Refractive index of cladding = 1.48

[3]
a.

Outline how the combination of core and cladding reduces the overall dispersion in the optic fibres.

[3]
b.

Markscheme

realization that 𝜃 min is the critical angle

𝜃 = «sin–1 \(\frac{{1.48}}{{1.5}}\) =» 80.6 «°»

Accept 1.4 rad

β = «90 – 80.6 =» 9.4 «°»

Accept 0.16 rad

a.

because the critical angle is nearly 90°

then only rays that are «almost» parallel to the fibre pass down it

so pulse broadening is reduced

OWTTE

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Option C: Imaging » Option C: Imaging (Core topics) » C.3 – Fibre optics
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