1. Paraffin wax is represented by
a) C18H35
b) C18H40
c) C18H36
d) None of the mentioned
Explanation: Paraffin wax in a semi solid stage is represented by C18H38.
2. A thermoplastic material has a linear polymer chain while a thermosetting plastic has a crosslinked polymer chain.
a) True
b) False
Explanation: Given statement is true thats why thermoplastic can be remoulded while thermosettings can’t be.
3. Which of the following is a thermosetting polymer?
a) PVC
b) PTFE
c) Nylon
d) Polyesters
Explanation: a), b) and c) consist of linear structures while polyester consists of cross linked and hence is a thermosetting polymer.
4. Teflon has very high coefficient of resistance.
a) True
b) False
Explanation: Teflon is very smooth and has coefficient of friction as low as 0.04.
5. Viscoelastic materials at low temperatures show no change in its strain with change in stress.
a) True
b) False
Explanation: Viscoelastic materials follow Hooke’s law at intermediate temperatures.
6. Which of the following property is affected by heat treatment?
a) Hardness
b) Strength
c) Ductility
d) All of the mentioned
Explanation: Heat treatment involves changes in the micro structure and hence all the internal properties are effected.
7. Annealing involves heating the component to a temperature
a) Slightly above the critical temperature
b) Equal to critical temperature
c) Slightly less than critical temperature
d) None of the mentioned
Explanation: In annealing, component is heated to a temperature above than critical temperature.
8. Which of the following is true?
a) Rate of cooling in normalising is faster then in annealing
b) Annealing improves ductility
c) Normalising improves grain structure
d) All of the mentioned
Explanation: In annealing, the furnace is switched off and component cools slowly. In normalising, component is air cooled.
9. Tempering involves
a) Reheating the quenched component to a temperature greater than critical temperature
b) Increases the brittleness
c) Reheating the quenched component to a temperature equal to critical temperature
d) None of the mentioned
Explanation: Tempering involves reheating the quenched product to a temperature less than transformation range. It improves ductility and reduces brittleness
10. Silicon addition in spring steel increases its toughness
a) True
b) False
Explanation: Silicon addition increases strength without lowering the ductility.