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Question 19N.3.SL.TZ0.9

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Date November 2019 Marks available [Maximum mark: 5] Reference code 19N.3.SL.TZ0.9
Level SL Paper 3 Time zone TZ0
Command term Describe, Determine, State Question number 9 Adapted from N/A
9.
[Maximum mark: 5]
19N.3.SL.TZ0.9

Communication signals are transmitted over long distances through optic fibres.

(a)

Describe why a higher data transfer rate is possible in optic fibres than in twisted pair cables.

[2]

Markscheme

fibres have broader bandwidth than cables ✔
therefore can carry multiple signals simultaneously ✔

A signal is transmitted along an optic fibre with attenuation per unit length of 0.40 dB km–1. The signal must be amplified when the power of the signal has fallen to 0.02 % of the input power.

(b(i))

State one cause of attenuation in the optic fibre.

[1]

Markscheme

absorption/scattering of light
OR
impurities in the «glass core of the» fibre ✔

(b(ii))

Determine the distance at which the signal must be amplified.

[2]

Markscheme

attenuation = 10 log2×10-4=-37 «dB» ✔
amplification required after 370.4=92 or 93 «km» ✔
NOTE: Allow ECF from mp1 for wrong dB value.(eg: 42 km if % symbol ignored).

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