The input power to a single optic fibre X is 25 mW. The signal needs to be amplified when the power has been attenuated to 4.0 ×10^–19 W. The attenuation loss in the optic fibre is 1.8 dB km^–1.

Calculate the maximum distance between amplifiers in the system.

$\frac{I}{{{I_0}}} = 101{\rm{g}}\left[ {\frac{{25 \times {{10}^{ - 3}}}}{{4 \times {{10}^{ - 19}}}}} \right]\left( { = 168} \right)$;
$\frac{{168}}{{1.8}}$;
93 km;