This set of Design of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “High Conductivity Materials”.
1. Which material has the highest conductivity of all materials?
a) Silver
b) Copper
c) Gold
d) Tungsten
View Answer
Explanation: On a scale of 100, silver has 100 percent on high conductivity, copper has 97. When compared to silver and copper gold has only 76 percent. Tungsten is not a material of this group.
2. High conductivity materials are used in electrical machines.
a) True
b) False
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Explanation: These materials have low resistivity. Hence they allow for the good flow of current, which in turn allows the proper operation of the machine.
3. What are the characteristics of high conductivity materials based on cost and flexibility?
a) Low cost, low flexibility
b) Low cost, high flexibility
c) High cost, low flexibility
d) High cost, high flexibility
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Explanation: Cost should be always less, in order to help in purchase of many quantities of the material for more applications. It should also be highly flexible, in order to mould according to people’s choice.
4. What is the temperature coefficient of silver?
a) 0.00386 per0C
b) 0.0034 per0C
c) 0.00429 per0C
d) 0.0038 per0C
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Explanation: 0.0034 per0C relates to the temperature coefficient of Gold, whereas 0.00429 per0C is the temperature coefficient of Aluminum. 0.00386 per0C corresponds to temperature coefficient of Copper.
5. Silver is not used in practical electrical machines.
a) True
b) False
View Answer
Explanation: Silver has lots of properties which can make it suitable to be used in practical use. But the high cost factor which occurs to Silver makes it used only for important instruments.
6. What is the conductivity of Copper?
a) 0.6329*106 mho/cm
b) 0.5952*106 mho/cm
c) 0.4529*106 mho/cm
d) 0.3773*106 mho/cm
View Answer
Explanation: 0.6329*106 mho/cm relates to the conductivity value of Silver. 0.4529*106 mho/cm relates to the conductivity value of Gold and 0.4529*106 mho/cm relates to the conductivity value of Aluminum.
7. What is the melting point of aluminum?
a) 6600C
b) 10850C
c) 9620C
d) 10640C
View Answer
Explanation: 6600C is the melting point of Aluminum. 9620C relates to the melting point of Silver and 10850C is the melting point of Copper.
8. What is the specific gravity of aluminum?
a) 8.96 gm/cm3
b) 19.30 gm/cm3
c) 2.70 gm/cm3
d) 10.49 gm/cm3
View Answer
Explanation: 8.96 gm/cm3 is the specific gravity of Copper. 19.30 gm/cm3 relates to the specific gravity of Gold and 10.49 gm/cm3 is the specific gravity of Silver.
9. Which two elements are used in precious instruments?
a) Copper, Silver
b) Gold, Silver
c) Copper, Aluminum
d) Gold, Aluminum
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Explanation: Silver is used only in precious instruments because of its high cost. Gold, on the other hand, is not only costly but also not suitable for many practical applications and can lose its properties easily.
10. Which property of aluminum it the most preferred element?
a) good conductivity
b) highly malleable, highly ductile
c) most abundant element
d) good corrosion resistant
View Answer
Explanation: All the other elements among Silver, Copper, Gold have the other 3 properties along with Aluminum. But all the above mentioned materials are not highly abundant, which is also an important factor.
Sanfoundry Global Education & Learning Series – Design of Electrical Machines.
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