Question

Problem 92. A) Why do pulses that enter an optical fiber at the same time but at different angles, exit the fiber at dif- ferent times? B) Would a pulse in an optical fiber spread if the wave speed was the same for all frequency components? Briefly justify your answer. Problem 93. Do some internet research and then answer the following questions. A) What are the carrier frequencies and bandwidths associated with the 802.11ac wireless internet (WiFi) standard? B) What is the frequency range used by "over the air" VHF channels 2-13 in the United States?

Answer 1

Solution -

92 a)

The light will exit at different times when it enters at the different incident angles because at different angle of incidence the angle of refraction will be different and hence it directly impacts the path covered by the light .

If the angle of incidence is higher (keep the light source constant of particular wavelength ) then the angle of refraction will be higher and hence light will move with least distance with less number of total internal reflections and will exit early , In contrast of this if the angle of incidence is lower so the angle of refraction will be lower and hence light will travel long inside the optical fiber because of more number of internal reflections faced and will emerge out taking long time .

2. No , it would not spread . The reason for spread of light into components is the different velocity of the components in a particular medium . Like in prism the wave with higher wavelength refracts less because it's speed is more in that medium and vice versa. So if the speed is same for all the components then they all will have the same angle of refraction and will move in coherent way without spreading.

93 solution -

1. Ans

Frequency - 5.8GHz

802.11ac works exclusively in the 5GHz band, uses plenty of bandwidth (80 or 160MHz), operates in up to eight spatial streams (MIMO).

2. VHF band which comprises channels 2 through 13 and occupies frequencies between 54 through 216 MHz, and the UHF band, which comprises channels 14 through 51 and occupies frequencies between 470 and 700 MHz.

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