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.
resistance is 0.7 ohms per km
current is 0.8A for the whole circuit (treating it as series.)
power loss = I^2 R