| 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 | Outline | 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.
