1. Do amorphous materials display the phenomenon of polymorphism? Why or why not
(Explain very briefly)?
2. Very briefly discuss two similarities and two differences between photons and phonons
3. The loss of an optical fibre is measured by the cutback technique. The output power at
1550 nm wavelength after 18 km is measured to be 6 m W. The fibre is then cut back to 1
km length and the output power is measured to be 18 mW.
(a) Calculate the loss of the fibre at 1550 nm in dB/km.
(b) Assuming that this loss value is only due to Rayleigh scattering, calculate the loss of this
fibre at wavelengths of 1300 nm and 1000 nm.
1. You have been given a sample and asked to find out whether it is crystalline or non-
crystalline, if non-crystalline whether it is amorphous or glass and also the actual
elemental composition. What different sequential choracterisations you will perform to
find the above and also mention the key observation from these characterisations. You can
show this in the form of a flow-chort.
2. Two glasses of same composition (Glass a and Glass b) have been prepared by cooling a
melt at 200 K/min and 400K/min, respectively.
Which glass has higher density? Qualitatively explain briefly why this is the case by
showing or drawing a schematic of Volume Vs Temperature critical cooling curves,
displaying at least two cooling rates.
Between these two glasses, which one has lower Rayleigh scattering based optical loss and
explain briefly why based on the same schematic.
3. The table below lists the characteristic temperatures for various glasses measured by DTA.
Calculate the "glass forming ability" based on Hruby parameter for these glasses. Which
having the best glass forming ability and arrange them in the ascending order of glass
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Polymorphism relates to different forms in which a solid can exist, usually with some crystal structure, with possible admixture of some amorphous fraction.
Since polymorphism is about different crystal structures, it cannot exist in amorphous materials.
We note however that there is an analogous polyamorphysm for amorphous materials which relates to different amorphous states of the same material. There are examples of polymers, liquids, and glasses...