Fibre
optics
1. What is
meant by total internal reflection?
2. Describe
the construction of two sorts of fibres used in fibre optics, illustrating your
answer with diagrams.
3. What is
the approximate range of diameters of monomode fibres?
4. Why can you
bend thin glass fibres without them breaking where if you attempted to do this
with thick ones they would shatter?
5. Apart from
the danger of breaking why is there a limiting angle for the bending of glass
fibres if they are still to be useful?
6.
Describe carefully three uses of fibre optics.
7.
Explain at least one advantage of using one of the applications that you
mentioned in question 1.
8.
Does a greater difference between the refractive index of the fibre and that of
the surrounding air give a greater or smaller critical angle?
9.
In view of your answer to number 3, why is the fibre surrounded by a layer of
glass cladding? (at least three reasons are required here).
10.
Which has the higher refractive index, the central fibre or the cladding?
11.
What is the critical angle between a glass fibre refractive index 1.5 and air,
refractive index 1.00?
12.
What is the critical angle between a glass fibre refractive index 1.5 and glass
cladding? (a) for a difference in the refractive index of the fibre and that of
the cladding of 0.05
(b)
for a difference in the refractive index of the fibre and that of the cladding
of 0.01
(c)
for a difference in the refractive index of the fibre and that of the cladding
of 0.1
13. A glass
fibre of diameter 0.01 mm and 1 km long is used to transmit a light beam. What
is the maximum difference in distance between a ray of light that makes no
reflections with the fibre walls and one that makes the most possible
reflections if the refractive index of the fibre and the cladding are the same
as those given in question seven?
14. In the
observation of internal organs of the body, for example, why must the bundle of
fibres not be twisted relative to each other?
15. Draw an
accurate diagram to show a ray of light meeting the centre of the end of a
straight glass fibre at an angle of incidence of 40o and entering
the glass. For a difference between the refractive index of the core and the
cladding prove whether or not this ray will be totally internally reflected and
travel down the fibre.
16. Explain
with the help of a diagram what is meant by multipath dispersion.
