Page 337 - Physics Coursebook 2015 (A level)

Chapter 20: Communications systems
5 a Describe the orbit of a geostationary satellite. [2] b State a typical wavelength for communication between the Earth’s surface and a geostationary satellite. [1] c State one advantage and one disadvantage of the use for telephone communication of a geostationary
satellite compared with a satellite in polar orbit. [4]
6 Figure 20.15 shows a coaxial cable.
a State and explain the purpose of the fine woven copper wire or braid. [2]
b Optic fibre has a larger bandwidth than a coaxial cable. Explain why increased bandwidth has reduced
the cost of telephone calls to distant countries. [1]
c i Explain what is meant by electrical noise. [1] ii State two causes of noise in a copper cable. [2]
7 Radio signals may be transmitted by surface (ground) waves, by space waves or by sky waves. State a typical
value for the frequency and the maximum distance of transmission for each type of wave. [6]
8 Figure 20.20 shows an amplitude-modulated radio wave carrying a signal.
80 μs 80 μs
Figure 20.20 For End-of-chapter Question 8.
a Determine the radio frequency of the carrier wave. [2]
b Calculate the frequency of the signal. [2]
c Draw the frequency spectrum of the modulated radio wave [3]
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