13. For Fresnel loss at an interface, which of these is the fraction of light reflected at the interface? a) r= (na+ nb)/(na.nb) b) r= (na-nb)/(n+ nb) c) r= (nb-n)/(n-n) d) r- (no-n)/(n-n) 14. The primary design criteria for fiber optic link are a) Bit rate and link length b) Link length and noise level c) Noise level and bit rate d) Bit rate, noise level and link length 15. The additional parameters required for a successful fiber link design are a) 4 b) 6 c) 5 d) 3 e) 2