Electrical Engineering Materials MCQs ( Design Of Electrical Machines ) MCQs – Competitive Design Of Electrical Machines MCQs
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Design Of Electrical Machines MCQs – Electrical Engineering Materials MCQs ( Design Of Electrical Machines ) MCQs
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Electrical Conducting Materials
1. What is the basic property of electrical conducting materials?
a) allows the passage of current through the materials
b) blocks the passage of current through the materials
c) leaks the current through the materials
d) reverses the direction of current in the materials
Answer: a
Explanation: The basic property of conducting materials is to allow the flow of charges, and align them in a particular direction. The process is nothing but the flow of current in the materials.
2. What is the correct classification of the conducting materials?
a) low resistivity, low conductivity
b) low resistivity, high conductivity
c) high resistivity, high conductivity
d) medium resistivity, medium conductivity
Answer: b
Explanation: Resistivity is inversely proportional to the conductivity. So, if the material consists of high resistivity then it will obviously have low conductivity and vice versa.
3. Example of low resistivity material is _____________
a) silver
b) manganese
c) magnesium
d) tungsten
Answer: a
Explanation: Silver is the low resistivity material of all given materials. Tungsten is a part of high resistivity materials. The other two materials do not have a fixed resistivity and they vary with temperature.
4. Example of high resistivity material is ________________
a) copper
b) gold
c) aluminum
d) carbon
Answer: d
Explanation: Carbon is the highly resistivity material of all the materials. Whereas the other 3 materials are associated with low resistivity property in nature.
5. High resistivity material used in making the filaments of incandescent lamps.
a) true
b) false
Answer: a
Explanation: It is because to protect the lamps from getting over-heated. If the filaments get over-heated, it can lead to the bursting of the lamps.
6. What materials are used as conductors in the Transmission and Distribution sector?
a) copper
b) silver
c) tungsten
d) carbon
Answer: a
Explanation: Conductors in power system require less resistivity, highly malleable, highly ductile and less cost. Silver has all the above properties, but it is highly costly. So that makes copper highly suitable.
7. What are the properties of Conducting Materials with respect to temperature coefficient of resistance and tensile strength?
a) low temperature coefficient, low tensile strength
b) low temperature coefficient, high tensile strength
c) high temperature coefficient, low tensile strength
d) high temperature coefficient, high tensile strength
Answer: b
Explanation: The resistance of the material should not increase with temperature rise. This can lead to the loss of conduction property. High tensile strength allows in withstanding external disturbances, for smooth functioning.
8. What are the conditions of the conducting materials with respect to melting point and resistance to corrosion?
a) high melting point, low resistance to corrosion
b) low melting point, low resistance to corrosion
c) high melting point, high resistance to corrosion
d) low melting point, high resistance to corrosion
Answer: c
Explanation: High melting point, allows the materials to withstand low temperatures. High resistance to corrosion allows the material to avoid corrosion, to conduct effectively.
9. How should the conducting materials be in terms of malleability and ductility?
a) highly malleable, less ductile
b) less malleable, less ductile
c) highly malleable, highly ductile
d) less malleable, highly ductile
Answer: c
Explanation: The materials, having high malleability allow smooth conduction in transmission and distribution. The materials having high ductility help in producing wires flexibly for conduction.
10. Aluminum has high conductivity than Copper.
a) true
b) false
Answer: b
Explanation: Copper has high conductivity than Aluminum. The conductivity of Copper is 58.14*106 s/m and the conductivity of aluminum is 37.2*106 s/m.
High Conductivity Materials
1. Which material has the highest conductivity of all materials?
a) Silver
b) Copper
c) Gold
d) Tungsten
Answer: a
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
Answer: a
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
Answer: b
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
Answer: d
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
Answer: a
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
Answer: b
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
Answer: b
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
Answer: c
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
Answer: b
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
Answer: c
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.
Magnetic Materials
1. What is the property of magnetic materials?
a) Resistivity
b) Conductivity
c) Permeability
d) Ductility
Answer: c
Explanation: There are many properties of magnetic materials, and permeability is one among them. The other 3 properties are related to other materials like conducting and insulating materials.
2. What is the property of permeability in magnetic materials?
a) how easily the magnetic flux is broken/clear
b) how easily the magnetic flux is set up
c) how long the magnetic flux takes to form
d) how long the magnetic flux takes to clear
Answer: b
Explanation: The basic operation of magnetic material is to form magnetic flux. Permeability is the ability of the material to determine how easily the magnetic flux is set up.
3. What is the representation of permeability?
a) coercivity/retentivity
b) flux/flux density
c) magnetic force/magnetic flux density
d) magnetic flux density/magnetic force
Answer: d
Explanation: Permeability is the property which deals, with the relationship with magnetic flux density and magnetic force. Magnetic force/Magnetic flux density deals with the reciprocal of permeability. Coercivity/Retentivity deals with the terms of B-H curve.
4. How should the permeability and number of ampere turns for good magnetic materials be?
a) high permeability, high ampere turns
b) high permeability, low ampere turns
c) low permeability, low ampere turns
d) low permeability, high ampere turns
Answer: b
Explanation: High permeability is always required in magnetic materials for its good operation. At the same time high permeability leads to less ampere turns in the materials.
5. Is retentivity associated with B-H curve?
a) Yes
b) No
Answer: a
Explanation: B-H curve deals with the concepts of retentivity and coercivity. The property of retentivity can be shown in the B-H curve by an increasing curve in the curve.
6. What is the property of retentivity in magnetic materials?
a) After removal of external magnetic fields, magnetization exists
b) After removal of external magnetic fields, magnetization doesn’t exist
c) After removal of internal magnetic fields, magnetization exists
d) After removal of internal magnetic fields, magnetization doesn’t exist
Answer: a
Explanation: Magnetic materials have the property of retentivity in which the magnetic flux produced acts according to the external magnetic field. When the external field is removed, the magnetization in the materials doesn’t deform immediately.
7. What is coercivity force in magnetic materials?
a) The force required to add upon the existing magnetization
b) The force required to remove the existing magnetization
c) The force required to produce magnetic flux
d) The force required to break magnetic flux
Answer: b
Explanation: Magnetic materials generally have the property of retaining magnetization, even if the external magnetic field is removed. So, coercive force is the force that is required to reduce the magnetization.
8. What are magnetic hard materials?
a) High retentivity, low coercivity
b) High retentivity, high coercivity
c) Low retentivity, low coercivity
d) Low retentivity, high coercivity
Answer: b
Explanation: High retentivity is required for protecting the magnetic materials from losing its magnetic property. High coercivity is required to reduce the effect of retentivity to protect the material.
9. What is reluctance in magnetic materials?
a) Allows the buildup of magnetic flux
b) Reduces the buildup of magnetic flux
c) Resists the buildup of magnetic flux
d) Increases the buildup of magnetic flux
Answer: c
Explanation: Reluctance, as the name suggests, is something which is reluctant or hesitant to do. As per the magnetic terms it resists the building up of magnetic flux in the materials.
10. High Reluctance affects the performance of magnetic materials.
a) True
b) False
Answer: a
Explanation: High reluctance means the materials resist in building up the magnetic flux to a higher extent. So, for the proper functioning the reluctance values should be as low as possible.
11. What is the unit of reluctance in magnetic materials?
a) Henry/m
b) Weber/m2
c) Ampere-turns/Weber
d) Ampere-turns/m
Answer: c
Explanation: Henry/m deals with the unit of permeability. Weber/m2 deals with the unit of magnetic field. Reluctance is the opposite of permeance.
12. How many classifications of magnetic materials are present?
a) 3
b) 4
c) 5
d) 6
Answer: c
Explanation: There are basically 4 properties in magnetic materials and 5 classifications. They are diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic, ferrimagnetic.
13. What is the property of ferromagnetic materials?
a) Negative magnetization
b) Magnetization slightly less than 1
c) Magnetization slightly greater than 1
d) Magnetization very much higher than 1
Answer: d
Explanation: Negative magnetization denotes the property of Diamagnetic materials. Magnetization slightly greater than 1 denotes the property of Paramagnetic materials. Ferromagnetic materials have magnetization in the range of 1000+.
14. What is the example of diamagnetic materials?
a) Quartz
b) Pyrite
c) Montmorillonite
d) Biotite
Answer: a
Explanation: The other 3 materials are paramagnetic in nature, which means magnetization is slightly above 1. Quartz is a diamagnetic material in which the magnetization is negative.
15. What is the example of ferromagnetic materials is?
a) Magnetite
b) Hematite
c) Nickel
d) Biotite
Answer: a
Explanation: Hematite denotes the example of antiferromagnetic materials. Nickel denotes an example of ferromagnetic materials. Biotite denotes the example of paramagnetic materials.
Insulating Materials
1. What is the property of insulating materials?
a) Prevents the unwanted flow of current
b) Allows the unwanted flow of current
c) Increases the unwanted flow of current
d) Decreases the unwanted flow of current
Answer: a
Explanation: Conductors, allow the flow of current through the material. Insulators are the opposite of conductors. The material doesn’t allow the flow of current through them.
2. In the Transmission and Distribution sector, where should the insulators be placed?
a) Between towers and poles
b) Between towers and ground
c) Between towers and conductors
d) Between conductors and ground
Answer: c
Explanation: The insulators are used to block the flow of unwanted current. In power system, already the tower and the conductors are grounded. Thus the insulators are connected between towers and conductors.
3. What is the main cause for the failure of overhead line insulators?
a) Surges
b) Flashover
c) Arching
d) Grounding
Answer: b
Explanation: In overhead lines, there occurs a flow of abnormal over voltages. This abnormal over voltages, causes flashover. This flashover causes damage to overhead line insulators.
4. What happens when some serious phenomenon occurs in the insulators?
a) Puncher is produced in the insulator body
b) Insulator body bulges
c) Insulator body bursts
d) Insulator body tears apart
Answer: a
Explanation: The serious phenomenon is the abnormal over voltage, produced in the insulators. Due to that, flashover occurs in the insulators. This causes puncher of the insulator body.
5. Insulation Resistance should be high in insulators.
a) True
b) False
Answer: a
Explanation: Insulation Resistance is very important in the performance of insulating materials. If the insulation resistance becomes low, high flow of current occurs and can damage the material.
6. How should the properties of strength and dielectric strength in insulating materials?
a) High strength, low Dielectric strength
b) Low strength, low Dielectric strength
c) High strength, high Dielectric strength
d) Low strength, high Dielectric strength
Answer: c
Explanation: The insulator should have high strength in order to prevent the insulating materials. The insulator should have high dielectric strength, in order to hold the electric field without breaking down.
7. What is property of porosity and temperature change in insulating materials?
a) Less, less affected
b) Less, highly affected
c) High, highly affected
d) High, less affected
Answer: a
Explanation: The insulating materials should have less porosity as it should not lose the internal properties due to holes. The material should also be less affected by temperature change in order to preserve its properties.
8. What is the dielectric strength of porcelain insulators?
a) 60 kV/cm
b) 140 kV/cm
c) 50 kV/cm
d) 40 kV/cm
Answer: a
Explanation: Porcelain has a dielectric strength of 60kV/cm. 140 kV/cm denotes the dielectric strength of glass insulator.
9. What is the dielectric strength, coefficient of thermal expansion of glass with respect to porcelain insulators?
a) High, high
b) High, low
c) Low, low
d) Low, high
Answer: b
Explanation: Glass has a higher dielectric strength (140 kV/cm) when compared to porcelain (60 kV/cm) and glass has a lower coefficient of thermal expansion when compared to porcelain.
10. Glass has lower tensile strength compared to porcelain insulators.
a) True
b) False
Answer: b
Explanation: Glass insulators have all properties better than that of porcelain. Glass has high dielectric strength, low coefficient of thermal expansion and then High tensile strength than that of porcelain.
11. What is the other name of Polymer Insulator?
a) Moisture insulator
b) Core insulator
c) Composite insulator
d) Mixed insulator
Answer: c
Explanation: It is also known as composite insulator. It is known as composite insulator because it consists of both core and the weather sheds in them.
12. How many classifications of overhead line insulators are there?
a) 3
b) 4
c) 5
d) 6
Answer: a
Explanation: There are basically 3 types of overhead line insulators. They are Pin type, Suspension type and Stray Insulator type.
13. How many types of electrical insulators are present on the basis of voltage application?
a) 2
b) 3
c) 4
d) 5
Answer: a
Explanation: There are two types of insulators based on voltage application. They are Stay Insulators and Shackle Insulators.
14. How many discs are used in suspension insulators for 220kV?
a) 3
b) 4
c) 8
d) 14
Answer: d
Explanation: 3 discs are used when voltage is 33kV. 4 discs are used when voltage is 66kV. 8 discs are used when voltage application is 132kV.
15. What is the other name of the shackle insulator?
a) String
b) Hanging
c) Spool
d) Post
Answer: c
Explanation: String is the other name of strain insulators, whereas, hanging is the other name of suspension insulators. Post insulator is otherwise Pin insulators.
Temperature Rise and Insulating Materials
1. How many number of insulation classes are present with respect to electrical equipment?
a) 5
b) 6
c) 7
d) 8
Answer: c
Explanation: There are 7 classes of insulation with respect to electrical equipment. They are Class Y, Class A, Class E, Class B, Class F, Class H, Class C.
2. How many classes have their temperatures above 100°C?
a) 5
b) 6
c) 7
d) 8
Answer: b
Explanation: There are 7 insulation classes present in relation with temperature. Of the 7 classes, there are 6 classes whose temperatures are greater than 100°C. Class Y is the only class having temperature less than 100.
3. How many classes have their temperatures above 150°C?
a) 2
b) 3
c) 4
d) 5
Answer: b
Explanation: Of 7 classes of insulation, there are 3 classes whose temperatures are above 150°C. They are classes F, H, C of insulation.
4. Which class has the lowest and the highest temperature?
a) Class Y, Class C
b) Class Y, Class H
c) Class H, Class C
d) Class B, Class H
Answer: a
Explanation: Class Y belongs to the lowest insulation class of having temperature of about 90°C. Class C is the highest insulation class of having temperature above 180°C.
5. Class A has higher temperature than Class E.
a) True
b) False
Answer: b
Explanation: Class E has a higher temperature than that of Class A. The temperature of Class A is 105°C and the temperature of Class E is 120°C.
6. What is the temperature of Class B?
a) 120°C
b) 130°C
c) 155°C
d) 180°C
Answer: b
Explanation: 120°C refers to the temperature of Class E. 155°C refers to the temperature of Class F. 180°C refers to the temperature of Class H.
7. Which among the following is the example of Class Y?
a) Varnish
b) Insulation oil
c) Paper
d) Resins
Answer: c
Explanation: Varnish is an example of Class A. Even insulation oil is an example of Class A. Resins is an example of Class E.
8. Which among the following is the example of Class B?
a) Inorganic material with adhesives
b) Hard fiber
c) Wood
d) Impregnated oil
Answer: a
Explanation: Impregnated oil is the example of Class H. Hard Fiber is the example of Class Y and Wood is the example of Class A.
9. Which among the following is an example of Class F?
a) Paper lamination
b) Nitrile rubber
c) Asbestos
d) Silicone
Answer: d
Explanation: Paper lamination is the example of Class E. Nitrile Rubber is the example of Class A. Asbestos is the example of Class B.
10. Silicone rubber is an example of Class H.
a) True
b) False
Answer: a
Explanation: Class H is one of the insulation classes having temperature about 180°C. Silicone rubber is one of the examples of Class H.