Answer:
Telegraph distance will be 9.6 mile
Explanation:
We have given the voltage V = 9 volt
Contact resistance = 4 ohm
Relay resistance = 80 ohm
And wire has a resistance = 10 ohm/mile
We have given the current = 50 mA =0.05 A
According to ohm's law [tex]R=\frac{V}{I}=\frac{9}{0.05}=180ohm[/tex]
So the resistance of wire = 180-4-80=96 ohm
So the length of the telegraph distance will be [tex]\frac{96}{10}=9.6mile[/tex]