Read the following... after which there are some questions which
I am unsure of.
Transmission of light through fiber optics is not 100%
efficient since light is absorbed by impurities in glass. If light
travels over 75km of glass, then only 10% of the signal arrives at
the other end. Over long distances, light signal has to be boosted
by underwater repeaters that are powered by an electric current
sent along a metal sheath inside the cable. The repeaters are
connected in series with the same current of 0.80A through each and
a potential difference of 40V across each repeater. In a
typical 7500km undersea cable there are 100 repeaters. Each
kilometre of the metal sheath has a resistance of 0.70ohm and some
of the energy provided by supply is lost as thermal energy (heat)
in the sheath.
Determine, for a 7500km uindersea cable,
(i) total potential difference across all repeaters
40 V X 100 = 4000V
(ii) total potential difference across resistance of metal
sheath
0.70 X 7500X 0.80 = 4200V
(iii) potential difference provided by power supply
4200 - 4000 = 200V
(iv) the thermal energy(heat) lost per second from each
kilometreof metal sheath.
(i have no idea how to go about doing this)
I ain't sure whether I am right but I took a stab at the
questions anyway. Please assist. Thanks.