**Question:**

**(i) The intensity of a light pulse travelling along a communication channel decreases exponentially with distance x according to the relation I = Ioe–αx, where I o is **

**the intensity at x = 0 and α is the attenuation constant. Show that the intensity reduces by 75 per cent after a distance of (ln 4/α)**

**(ii) Attenuation of a signal can be expressed in decibel (dB) according to the relation dB =10 log10 (I/I0). What is the attenuation in dB/km for an optical fibre in **

**which the intensity falls by 50 per cent over a distance of 50 km?**

**Solution:**

(i) The decrease in the intensity is reduced by 75%.

(ii) The attenuation of the given optical fibre = 0.0602 dB/km