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A distance telephone whose resistance is 300 ohm is connected to the exchange,10 miles away , but a pair of telephone wires whose resistance,singly, is 5 ohm per mile. A twig falls across the wires at a certain point, producing the effect of a resistance R connected between the wires at that point. Measurements made at the exchange show a resistance between the terminals of the line of 130 ohm which rises to 160 ohm when the distant telephone is disconnected.  How far from the exchange is the fault to be found and what is the value of R?

Asked by mridulabarua05 11th February 2019, 1:20 PM
Answered by Expert
When the distance telephone is disconnected, measured resistance at telephone exchage shows the resistance of line wires
till the place where twig has fallen and the resistance R of the twig.
Here two variables are involved, (1) the distance from exchange to the place where twig has fallen and (2) the twig resistance.
Hence only from measured value of resistance at telephone exchange, we can not get both the distance and twig resistance.
If we know one variable, other one can be determined
Answered by Expert 12th February 2019, 12:16 PM
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