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Question 17N.3.HL.TZ0.15

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Date November 2017 Marks available [Maximum mark: 6] Reference code 17N.3.HL.TZ0.15
Level HL Paper 3 Time zone TZ0
Command term Calculate, Outline Question number 15 Adapted from N/A
15.
[Maximum mark: 6]
17N.3.HL.TZ0.15

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

(a)

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]

Markscheme

realization that 𝜃 min is the critical angle

𝜃 = «sin–1 1.48 1.5 =» 80.6 «°»

Accept 1.4 rad

β = «90 – 80.6 =» 9.4 «°»

Accept 0.16 rad

(b)

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

[3]

Markscheme

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

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