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An optical fibre communication system works on a wavelength of $1.3 \mu \mathrm{m}$. The number of subscribers it can feed, if a channel requires $20 \mathrm{kHz}$ are
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The correct answer is:
$1.15 \times 10^{10}$
Given, $\lambda=1.3 \mu \mathrm{m}=1.3 \times 10^{-6} \mathrm{~m}$
Bandwidth of channel, $B \bar{W}=20 \mathrm{kHz}=20 \times 10^{3} \mathrm{~Hz}$
Optical source frequency,
$f=\frac{c}{\lambda}=\frac{3 \times 10^{8}}{1.3 \times 10^{-6}}$
$=2.3 \times 10^{14} 1 \mathrm{Iz}$
$\therefore$ Number of channels, $n=\frac{f}{\mathrm{BW}}=\frac{2.3 \times 10^{14}}{20 \times 10^{3}}$
$=1.15 \times 10^{10}$
Bandwidth of channel, $B \bar{W}=20 \mathrm{kHz}=20 \times 10^{3} \mathrm{~Hz}$
Optical source frequency,
$f=\frac{c}{\lambda}=\frac{3 \times 10^{8}}{1.3 \times 10^{-6}}$
$=2.3 \times 10^{14} 1 \mathrm{Iz}$
$\therefore$ Number of channels, $n=\frac{f}{\mathrm{BW}}=\frac{2.3 \times 10^{14}}{20 \times 10^{3}}$
$=1.15 \times 10^{10}$
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