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Date May 2017 Marks available 2 Reference code 17M.3.SL.TZ1.8
Level Standard level Paper Paper 3 Time zone 1
Command term Calculate Question number 8 Adapted from N/A

Question

Communication signals are transmitted through optic fibres using infrared radiation.

State two advantages of optic fibres over coaxial cables for these transmissions.

[2]
a.i.

Suggest why infrared radiation rather than visible light is used in these transmissions.

[1]
a.ii.

A signal with an input power of 15 mW is transmitted along an optic fibre which has an attenuation per unit length of 0.30 dB km–1. The power at the receiver is 2.4 mW.

Calculate the length of the fibre.

[2]
b.

State and explain why it is an advantage for the core of an optic fibre to be extremely thin.

[2]
c.

Markscheme

longer distance without amplification

signal cannot easily be interfered with

less noise

no cross talk

higher data transfer rate

[2 marks]

a.i.

infrared radiation suffers lower attenuation

[1 mark]

a.ii.

loss = 10 log 2.4 15  «= −7.959 dB»

length = « 7.959 0.30 = » 26.53 ≈ 27 «km»

[2 marks]

b.

a thin core means that rays follow essentially the same path / OWTTE

and so waveguide (modal) dispersion is minimal / OWTTE

[2 marks]

c.

Examiners report

[N/A]
a.i.
[N/A]
a.ii.
[N/A]
b.
[N/A]
c.

Syllabus sections

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

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