This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Metallic Glasses”.
1. Which of the following is a metallic glass?
Explanation: Metallic glasses are amorphous metallic solids which have high strength, good magnetic properties and better corrosion resistance and will posses both the properties of metals and glasses. Of the following, only nickel is a metallic glass.
2. How are metallic glasses formed?
a) By increasing the rate of heating
b) By increasing the rate of cooling
c) By melting it
d) By rapidly heating and then cooling slowly
Explanation: Metals can be made into a glassy state by increasing the rate of cooling to a very high level. At that state the atoms will not be able to arrange orderly because of its rapid cooling rate. Thus, the atoms will not be allowed to go to crystalline state, rather it goes to amorphous state and it will form a new type of material. Such materials are called metallic glasses.
3. When does metal transform into the glass?
a) At Curie temperature
b) At critical temperature
c) At melting point of the metal
d) At glass transition temperature
Explanation: The temperature at which the metals in the molten form transforms into glasses is known as glass transition temperature. It is found that the glass transition temperature for metallic alloys varies from 20℃-300℃.
4. Which of the following is the most commonly used technique for the preparation of metallic glass?
a) Melt spinning system
b) Twin roller system
c) Melt extraction system
Explanation: Molten alloy is made to impinge on a fast rotating roller to form metallic glasses in melt spinning system. Whereas in other systems two or more steps are involved in the process making it tedious.
5. Quenching results in formation of metallic glasses.
Explanation: Quenching means rapid cooling. Actually atoms of any material move freely in a liquid state. Atoms can be arranged regularly when a liquid is cooled slowly. Instead, when a liquid is quenched, there will be an irregular pattern, which results in the formation of metallic glasses.
6. Which of the following is true about metallic glasses?
a) Low electrical resistance
b) Hexagonal closely packed structure
d) Low core loss
Explanation: Metallic glasses can be magnetised and demagnetised easily. They have very narrow hysteresis loop. They therefore exhibit very low hysteresis loss and hence transformer core loss is very less. They have high electrical resistance and Tetrahedral closely packed structure.
7. Metallic glasses cannot be used in cores of high power transformers.
Explanation: Since the metallic glasses possess low magnetic loss, high permeability, saturation magnetisation and low coercivity, these materials are used in cores of high power transformers.
8. When does a shape memory alloy return to its original shape?
a) At transition temperature
b) At Curie temperature
c) At memory transfer temperature
d) At normal temperature
Explanation: Shape memory alloys are those which change their shape from its original shape to a new shape and while heating or cooling it will come back to its original shape. This shape recovery process doesn’t happen at a single temperature but over a range of temperature. Thus, the range at which the SMA switches from new shape to its original shape is called transformation temperature or memory transfer temperature.
9. Why is NI-Ti alloy used in making eye frames?
a) Because they are hard
b) Because they are not flexible
c) Because they are hard to break
d) Because they are SMA
Explanation: NI-Ti alloys are shape memory alloys. Recently manufactured eye glass frames can be bent back and forth and can retain its original shape within fraction of time. All these materials are made up of NI-Ti alloys, which can withstand maximum deformation.
10. Can SMA be used to control and prevent fire?
Explanation: SMA is mainly used to control and prevent fire to a large extent. For example, an SMA is placed in a fire safety valve, when a fire occurs, due to the change in temperature the SMA changes its shape and shuts off fire.
11. Which of the following can be used to prepare nano-powder and nano-particles?
a) Sol-gel technique
b) Plasma arching
c) Chemical vapour deposition
d) Electro deposition
Explanation: Sol-gel process is based on hydrolysis of liquid precursors and formation of colloidal solutions. In every other technique, either only nano-powder or nano-particles can be formed. Only in sol-gel technique both nano-powder and nano-particles can be formed.
Sanfoundry Global Education & Learning Series – Engineering Physics.
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