# Multiple choice question for engineering

## Set 1

1. What is the formula for current in each of rotor bar?

a) current in rotor bar = 2 * slot pitch * window space factor * stator torque * stator current * power factor * rotor slots

b) current in rotor bar = 2 * slot pitch * window space factor / stator torque * stator current * power factor * rotor slots

c) current in rotor bar = 2 * slot pitch * window space factor * stator torque * stator current * power factor / rotor slots

d) current in rotor bar = 2 * slot pitch / window space factor * stator torque * stator current * power factor / rotor slots

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2. What is the relation between rotor mmf and stator mmf?

a) rotor mmf = 0.85 * stator mmf

b) rotor mmf = 0.80 * stator mmf

c) rotor mmf = 0.75 * stator mmf

d) rotor mmf = 0.70 * stator mmf

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3. What is the relation of the rotor resistance with respect to the starting torque?

a) rotor resistance is indirectly proportional to the starting torque

b) rotor resistance is directly proportional to the starting torque

c) rotor resistance is indirectly proportional to the square of the starting torque

d) rotor resistance is directly proportional to the square of the starting torque

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4.What is the relation of the rotor resistance to efficiency and losses?

a) as rotor resistance, losses increase, efficiency increases

b) as rotor resistance, losses increase, efficiency decreases

c) as rotor resistance, losses decrease, efficiency has no change

d) as rotor resistance, losses decrease, efficiency decreases

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^{2}R losses increases and cause heating effects. This increase in losses decreases the efficiency.

5. What is the relationship between current density, conductor area and resistance?

a) higher the current density, higher the conductor area, higher the resistance

b) higher the current density, higher the conductor area, lower the resistance

c) higher the current density, lower the conductor area, higher the resistance

d) lower the current density, lower the conductor area, lower the resistance

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6. What is the formula for the calculation of rotor resistance?

a) rotor resistance = resistance of the bars + resistance of end rings

b) rotor resistance = resistance of the bars – resistance of end rings

c) rotor resistance = resistance of the bars * resistance of end rings

d) rotor resistance = resistance of the bars / resistance of end rings

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7. What is the range of current density in rotor bars?

a) 4-9 A per mm^{2}

b) 4-6 A per mm^{2}

c) 4-7 A per mm^{2}

d) 5-6 A per mm^{2}

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^{2}. The maximum value of the current density in the rotor bars is 6 A per mm

^{2}.

8. What is the formula for the area of each bar?

a) area of each bar = current of the rotor bars + current density in rotor bars

b) area of each bar = current of the rotor bars / current density in rotor bars

c) area of each bar = current of the rotor bars * current density in rotor bars

d) area of each bar = current of the rotor bars – current density in rotor bars

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9. Can closed slots are preferred for small machines?

a) true

b) false

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10. What is the relation of closed slots with leakage reactance?

a) closed slots give no leakage reactance

b) closed slots give high leakage reactance

c) closed slots give low leakage reactance

d) closed slots give negative leakage reactance

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11. What is the relation of closed slots with leakage reactance and overload capacity?

a) closed slots give high leakage reactance, and increases the overload capacity

b) closed slots give high leakage reactance, and decreases the overload capacity

c) closed slots give low leakage reactance, and decreases the overload capacity

d) closed slots give low leakage reactance, and increases the overload capacity

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12. What is the relation between surface of rotor and the operation?

a) smooth surface leads to the quiet operation

b) rough surface leads to the quiet operation

c) smooth surface leads to the noisy operation

d) rough surface leads to the noisy operation

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13. Rectangular shaped bars and slots are preferred to circular bars and slots?

a) true

b) false

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14. What is the relation between clearances and slots?

a) high clearances are provided for salient slots

b) low clearances are provided for skewed slots

c) low clearances are provided for salient slots

d) high clearances are provided for skewed slots

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15. What is the range of clearance that can be left between rotor bars and the core?

a) 0.1-0.4 mm

b) 0.2-0.4 mm

c) 0.15-0.4 mm

d) 0.4-0.6 mm

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## Set 2

1. What is the work of the frame of dc machines?

a) to reduce the voltage

b) to reduce the flux

c) to carry the flux

d) to carry the current

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2. Why is the length of the yoke made larger?

a) to protect the armature windings

b) to cover the armature windings

c) to cover the field windings

d) to cover and protect the field windings

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3. What is the formula for the depth of the yoke?

a) depth of yoke = thickness/2

b) depth of yoke = thickness

c) depth of yoke = 2*thickness

d) depth of yoke = 3*thickness

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4.In large machines, the thickness is relatively larger to the diameter?

a) true

b) false

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5. What is the formula in order to check the rigidity?

a) moment of inertia ≥ (weight of magnetic frame * radius2 * 10-6) / 225

b) moment of inertia ≤ (weight of magnetic frame * radius2 * 10-6) / 225

c) moment of inertia = (weight of magnetic frame * radius2 * 10-6) / 225

d) moment of inertia < (weight of magnetic frame * radius2 * 10-6) / 225

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6. What is the formula for the thickness of the ac machines?

a) thickness = 40 * inner diameter of frame/12

b) thickness = 40 + inner diameter of frame/12

c) thickness = 40 – inner diameter of frame/12

d) thickness = 40 * inner diameter of frame*12

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7.What is the formula for the breadth of the ac machine?

a) breadth = 6 + 0.01 * inner diameter of frame

b) breadth = 6 – 0.01 * inner diameter of frame

c) breadth = 6 * 0.01 * inner diameter of frame

d) breadth = 6 / 0.01 * inner diameter of frame

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8. What is the formula for the checking of rigidity of induction machines?

a) moment of inertia ≥ radius / length of stator core * 90

b) moment of inertia ≥ radius * length of stator core * 90

c) moment of inertia ≥ radius * length of stator core / 90

d) moment of inertia ≤ radius / length of stator core * 90

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9. What is the formula for the radius at the centre of gravity?

a) radius at the centre of gravity = inner diameter1.5/ 6.3

b) radius at the centre of gravity = inner diameter2/ 6.3

c) radius at the centre of gravity = outer diameter1.5/ 6.3

d) radius at the centre of gravity = outer diameter2/ 6.3

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10. What is the formula of the centrifugal force?

a) centrifugal force = weight of revolving body * 39.43 * speed2* radius of circular path

b) centrifugal force = weight of revolving body / 39.43 * speed2* radius of circular path

c) centrifugal force = weight of revolving body * 39.43 / speed2* radius of circular path

d) centrifugal force = weight of revolving body * 39.43 * speed2 / radius of circular path

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## Set 3

1. What is the formula for number of turns in primary winding?

a) number of turns of primary winding = Voltage of primary windings * voltage per turn

b) number of turns of primary winding = Voltage of primary windings / voltage per turn

c) number of turns of primary winding = Voltage of secondary windings * voltage per turn

d) number of turns of primary winding = Voltage of secondary windings / voltage per turn

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2. What is the formula for obtaining the current in the primary winding?

a) current in primary winding = kVA per turn * 103 * primary voltage

b) current in primary winding = kVA per phase * 103 * primary voltage

c) current in primary winding = kVA per turn * 103 / primary voltage

d) current in primary winding = kVA per phase * 103 / primary voltage

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3. What does the area of conductors in primary and secondary windings depend on?

a) current

b) voltage

c) power

d) current density

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4. What does the permissible current density depend upon?

a) local heating

b) efficiency

c) output power

d) local heating and efficiency

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5. What is the relationship between temperature and the current density?

a) current density is directly proportional to the temperature

b) current density is directly proportional to the square of the temperature

c) current density is indirectly proportional to the square of the temperature

d) current density is indirectly proportional to the temperature

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6. What is the relationship between the losses and the maximum efficiency on the current density?

a) current density increases, losses decrease, efficiency increases

b) current density increases, losses increase, efficiency increases

c) current density decreases, losses decrease, efficiency increases

d) current density decreases, losses increase, efficiency increases

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7. What is the range of current density for small and medium power transformers?

a) 1-2 A per mm^{2}

b) 1-2.5 A per mm^{2}

c) 1.1-2.2 A per mm^{2}

d) 1.1-2.3 A per mm^{2}

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8. What is the range of current density for large power transformer with self oil cooled type?

a) 1-2 A per mm^{2}

b) 1.5-2.5 A per mm^{2}

c) 2.2-3.2 A per mm^{2}

d) 2-3 A per mm^{2}

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9. What is the condition for minimum loss condition?

a) current density in primary < current density in secondary

b) current density in primary > current density in secondary

c) current density in primary = current density in secondary

d) current density in primary >= current density in secondary

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10. The current density in relatively better cooled outer winding is made 10 percent greater than the inner winding?

a) true

b) false

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11. How many total high voltage windings are present?

a) 1

b) 2

c) 3

d) 4

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12. The low voltage windings are generally divided into 2 types?

a) true

b) false

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13. What is the rating for cylindrical type of winding with circular conductors?

a) 5000-10000 kVA

b) 5000-8000 kVA

c) 160-10000 kVA

d) 200-10000 kVA

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14. What is the voltage for cross over type of winding?

a) upto 15 kV

b) upto 33 kV

c) upto 66 kV

d) upto 6 kV

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15. What is the maximum current per conductor for helical winding?

a) from 12 A and above 12 A

b) from 300 A and above 300 A

c) upto 40 A

d) upto 80 A

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## Set 4

1. Which material has the highest conductivity of all materials?

a) Silver

b) Copper

c) Gold

d)Tungsten

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2. High conductivity materials are used in electrical machines.

a) True

b) False

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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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4. What is the temperature coefficient of silver?

a) 0.00386 per^{0}C

b) 0.0034 per^{0}C

c) 0.00429 per^{0}C

d) 0.0038 per^{0}C

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^{0}C relates to the temperature coefficient of Gold, whereas 0.00429 per

^{0}C is the temperature coefficient of Aluminum. 0.00386 per

^{0}C corresponds to temperature coefficient of Copper.

5. Silver is not used in practical electrical machines.

a) True

b) False

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6. What is the conductivity of Copper?

a) 0.6329*10^{6} mho/cm

b) 0.5952*10^{6} mho/cm

c) 0.4529*10^{6} mho/cm

d) 0.3773*10^{6} mho/cm

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^{6}mho/cm relates to the conductivity value of Silver. 0.4529*10

^{6}mho/cm relates to the conductivity value of Gold and 0.4529*10

^{6}mho/cm relates to the conductivity value of Aluminum.

7. What is the melting point of aluminum?

a) 660^{0}C

b) 1085^{0}C

c) 962^{0}C

d) 1064^{0}C

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^{0}C is the melting point of Aluminum. 962

^{0}C relates to the melting point of Silver and 1085

^{0}C is the melting point of Copper.

8. What is the specific gravity of aluminum?

a) 8.96 gm/cm^{3}

b) 19.30 gm/cm^{3}

c) 2.70 gm/cm^{3}

d) 10.49 gm/cm^{3}

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^{3}is the specific gravity of Copper. 19.30 gm/cm

^{3}relates to the specific gravity of Gold and 10.49 gm/cm

^{3}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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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

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## Set 5

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

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2. In 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

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3. What is the main cause for the failure of overhead line insulators?

a) Surges

b) Flashover

c) Arching

d) Grounding

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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

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5. Insulation Resistance should be high in insulators.

a) True

b) False

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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

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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

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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

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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

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10. Glass has lower tensile strength compared to porcelain insulators.

a) True

b) False

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11. What is the other name of Polymer Insulator?

a) Moisture insulator

b) Core insulator

c) Composite insulator

d) Mixed insulator

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12. How many classifications of overhead line insulators are there?

a) 3

b) 4

c) 5

d) 6

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13. How many types of electrical insulators are present on the basis of voltage application?

a) 2

b) 3

c) 4

d) 5

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14. How many discs are used in suspension insulators for 220kV?

a) 3

b) 4

c) 8

d) 14

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15. What is the other name of shackle insulator?

a) String

b) Hanging

c) Spool

d) Post