Question

16(2 points) Which of these monomers is the repeating unit for PTFE? a)FF b) H H C-C C-C H CH3 c) H H C-C НН d) H H C-C H CI 17 (2 points) Metals typically have a Poisson's ratio of: b) 0.3 c) 0.5 d) -0.35 18(2 points) Select a material which is an amorphous material a) Diamond b) Glass c) Steel d) Granite 19(2 points) The mobility of an electron is strongly affected by (circle all that apply)? a) Temperature b) Crystal structure c) Purity of material d) Applied electric field 20(2 points) Which of these polymers can be recycled (circle all that apply)? a) PE b) PVC c) PP d) PS

Answer 1

Answer 1)

PolyTetraFluoroEthylene (PTFE) as the name suggest is a polymer which contains repeated units of C2F2. It is also commonly known as Teflon. It is in solid state at room temperature and often used as non stick surfaces for cooking utensils due to its very low wettability. Monomer of this polymer is option a

Answer 2)

Poisson's ratio of a material gives the ratio of lateral strain and longitudinal strain. Materials with very high poisson's ratio can be pulled very easily and low poisson's ratio means that there is no tendency to get elongated. Metals do show some property of elongation and thus their poisson's ratio is around 0.3

Answer 3)

An amorphous material is defined as such material which has different physical properties(ex refractive index,etc,.) in different direction, so it means that they do not have a fixed long range order and their order change after short distances. They are also called glassy solid. Glass has amorphous material.

Answer 4)

Electron mobility refers to the tedency of electrons to quickly pass through a medium. If we increase the temperature the electrons velocity will increase and the number of collisions of the electrons with the atoms in the medium will also increase so, mobility decreases.

In semiconductors electron mobility may depend on the impurities present. These impurities can be in the form of acceptor or donor impurities.

Application of electric field will also change the electron mobility as the relation is given as -

electron mobility e = v/E , where E is electric field and v is the drift velocity.

Answer 5)

PE refers to PolyEthylene polymers. Here the repeating part is CH2-CH2 . It is one of the polymers picked up by recycling companies to recycle.

PVC refers to PolyVinylChloride. Here the repeating monomer is CH2-CHCl. Its an example of thermoplastic polymer. It is also very much recyclable.

PP refers to PolyPropylene. Here the repeating monomer is CH2-CH-CH3. It can be recycled but its recycling is not much economical than that of the other polymers.

PS refers to PolyStyrene. Here the repeating monomer is Ph - CH-CH2 . It is very difficult to recycle them.