# Multiple choice question for engineering

## Set 1

1. With what component is the output equation of DC machines related to?

a) power

b) voltage

c) current

d) losses

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2. What can be found out using the output equation of the DC machine?

a) main dimensions

b) angle of rotation

c) losses

d) efficiency

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3. What are the components of main dimensions of output equation of DC machine?

a) diameter

b) length

c) diameter and length

d) voltage

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4. What is the starting equation for deriving the output equation of DC Machines?

a) P = Generated Emf + Armature Current

b) P = Generated Emf – Armature Current

c) P = Generated Emf * Armature Current

d) P = Generated Emf / Armature Current

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5. The output equation of the DC machines can be used to calculate the speed of the machine?

a) true

b) false

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6. What is the output equation of DC machine?

a) Output power = Output Coefficient of the machine* Diameter^{2} * Length * Speed in rpm

b) Output power = Output Coefficient of the machine* Diameter^{2} * Length * Speed in rps

c) Output power = Output Coefficient of the machine* Diameter^{2} * Length / Speed in rps

d) Output power = Output Coefficient of the machine* Diameter^{2} * Length / Speed in rpm

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7. What are the terms related in deriving the output equation of the DC machine?

a) specific electric loading

b) specific magnetic loading

c) thermal coefficient of machine

d) specific electric and magnetic loading

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8. For a DC generator, what is the output power equation?

a) Output power = Generated Power * efficiency

b) Output power = Generated Power / efficiency

c) Output power = Generated Power – efficiency

d) Output power = efficiency / generated power

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9. For a DC motor, what is the output power equation?

a) Output power = Generated Power / efficiency

b) Output power = Generated Power * efficiency

c) Output power = Generated Power

d) Output power = Generated Power + efficiency

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10. For a DC generator, given D = 0.35 m, L = 0.21 m, Coefficient of output= 108.5, efficiency= 0.9, speed= 1400 rpm. What is the output power of the DC generator?

a) 65.12 W

b) 72.35 KW

c) 72.35 W

d) 65.12 KW

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## Set 2

1. What does the copper factor in PMDC motors represent?

a) it represents the armature circular area for conductors

b) it represents the field circular area for conductors

c) it represents the fraction of the armature circular area for conductors

d) it represents the fraction of the field circular area for conductors

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2. What is the range of the copper factor in PMDC motors?

a) 0.1-0.3

b) 0.1-0.2

c) 0.1-0.4

d) 0.2-0.4

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3. What is the formula for the armature resistance in PMDC motor?

a) armature resistance = (Diameter + length)*total number of armature conductors/1.2 * 104 * number of parallel paths in the armature2

b) armature resistance = (Diameter + length)*total number of armature conductors*1.2 * 104 * number of parallel paths in the armature2

c) armature resistance = (Diameter + length)*total number of armature conductors/1.2 * 104 + number of parallel paths in the armature2

d) armature resistance = (Diameter + length)+total number of armature conductors/1.2 * 104 * number of parallel paths in the armature2

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4. What happens to the diameter when the poles are more than 2?

a) diameter = 2 * diameter * (number of armature teeth embraced by one coil/total number of armature teeth)

b) diameter = 2.32 * diameter * (number of armature teeth embraced by one coil/total number of armature teeth)

c) diameter = 2.32 * diameter * (number of armature teeth embraced by one coil * total number of armature teeth)

d) diameter = 2 * diameter / (number of armature teeth embraced by one coil/total number of armature teeth)

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5. What factor does the permeance coefficient depend upon?

a) geometry of the magnet

b) geometry of the magnet, airgap, associated non-portions of the magnetic circuit

c) airgap

d) associated non-portions of the magnetic circuit

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6. What is the range of the permeance coefficient in the PMDC motors?

a) 3-5

b) 4-9

c) 4-8

d) 3-9

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7. What is the usual value of the permeance coefficient of the PMDC motor?

a) 4

b) 5

c) 6

d) 7

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8. The field current flowing in the conductor’s acts as demagnetizing force on the fraction tips of the magnet?

a) true

b) false

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9. What is the value of the demagnetizing coefficient if the total number of teeth is greater than 107?

a) d = angle/360

b) d = angle/240

c) d = angle/540

d) d = angle/720

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10. What is the value of the reluctance factor in the calculation of the intensity of magnetic field?

a) 1

b) 2

c) 1.15

d) 1,45

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11. What is the formula of the magnetic to electrical boarding ratio?

a) magnetic to electrical boarding ratio = number of poles * permeance coefficient * flux per pole/number of conductors * armature current

b) magnetic to electrical boarding ratio = number of poles / permeance coefficient * flux per pole*number of conductors * armature current

c) magnetic to electrical boarding ratio = number of poles + permeance coefficient * flux per pole/number of conductors * armature current

d) magnetic to electrical boarding ratio = number of poles * permeance coefficient / flux per pole*number of conductors * armature current

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12. How is the value of the magnetic to electrical boarding ratio related with the volume of iron and volume of copper?

a) high magnetic to electrical boarding ratio gives high copper volume and high iron volume

b) high magnetic to electrical boarding ratio gives low copper volume and high iron volume

c) low magnetic to electrical boarding ratio gives low copper volume and low iron volume

d) low magnetic to electrical boarding ratio gives low copper volume and high iron volume

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13. For good performance the small dc motor should have magnetic to electrical boarding ratio greater than 70?

a) true

b) false

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14.What is the formula for the flux density for the PM motors?

a) flux density = residual flux density / 1 + (1.11/permeance coefficient)

b) flux density = residual flux density * 1 + (1.11/permeance coefficient)

c) flux density = residual flux density / 1 + (1.11*permeance coefficient)

d) flux density = residual flux density * 1 + (1.11*permeance coefficient)

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## Set 3

1. How many design principles are present in the current transformers?

a) 2

b) 3

c) 4

d) 5

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2. What should be done in order to reduce the errors in the core?

a) armature mmf is to kept low

b) field mmf to be kept high

c) the exciting mmf is to be kept low

d) the field mmf is to be kept high

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3. How many classifications are the magnetic alloys used in the current transformers classified into?

a) 3

b) 2

c) 4

d) 5

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4. What is the material used in the transformer when the transformer errors should be small?

a) mumetal cores

b) steel cores

c) permender cores

d) presshamn cores

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5. What is the relation of the secondary winding leakage reactance and secondary circuit impedance?

a) secondary winding leakage reactance is directly proportional to the secondary circuit impedance

b) secondary winding leakage reactance is indirectly proportional to the secondary circuit impedance

c) secondary winding leakage reactance is directly proportional to the square of the secondary circuit impedance

d) secondary winding leakage reactance is indirectly proportional to the square of the secondary circuit impedance

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6. The ring shaped cores are made use of in the reduction of the secondary winding leakage reactance and secondary impedance?

a) true

b) false

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7. What type of core is employed when the performance standard required is not so high?

a) rectangular strips

b) c-shaped sections

c) rectangular strips or c-shaped sections

d) rectangular strips and c-shaped sections

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8. What should the magnetic path be in order to reduce the core reluctance?

a) length of the magnetic path in core should be low

b) length of the magnetic path in core should be medium

c) length of the magnetic path in core should be high

d) length of the magnetic path in core should be very high

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9. What is the value of the rated secondary current?

a) 1 A

b) 2 A

c) 3 A

d) 5 A

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10. What are the disadvantages of the low rated secondary current transformer?

a) high cost

b) high voltages

c) high voltages or high cost

d) high voltages and high cost

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11. What is the ideal condition with respect to the primary current rating?

a) ratio of secondary mmf to primary mmf should be high

b) ratio of secondary mmf to primary mmf should be low

c) ratio of excitation mmf to primary mmf should be high

d) ratio of excitation mmf to primary mmf should be low

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12. What is the rating of the primary current in the current transformer?

a) 200 A

b) 300 A

c) 400 A

d) 500 A

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## Set 4

1. How many design steps are available for the design of rotor?

a) 5

b) 6

c) 7

d) 8

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2. What is the main motive while choosing the number of rotor slots?

a) increasing the efficiency

b) decreasing the losses

c) no noise is produced

d) high output is produced

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3. What is the formula for the harmonic poles due to slots?

a) harmonic poles due to slots = 2 * (number of slots ± number of poles / 2)

b) harmonic poles due to slots = 2 / (number of slots ± number of poles / 2)

c) harmonic poles due to slots = 2 * (number of slots ± number of poles * 2)

d) harmonic poles due to slots = 1/ 2 * (number of slots ± number of poles / 2)

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4. What factors are used fixing the number of stator slots?

a) winding arrangement

b) number of poles

c) winding arrangement or number of poles

d) winding arrangement and number of poles

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5. Which condition satisfies the quiet operation in machines?

a) number of stator slots is divisible by number of pairs of poles

b) number of rotor slots differs from the number of stator slots by more than the number of poles

c) number of rotor slots is not divisible by number of pairs of poles

d) number of stator slots differs from the number of rotor slots by more than the number of poles

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6. What among the following are considered for the selection of number of rotor slots?

a) magnetic locking

b) cusps

c) magnetic locking or cusps

d) magnetic locking and cusps

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7. What is the formula for the total stator copper section for main winding?

a) total stator copper section for main winding = number of turns in the running winding * area of the running winding conductor

b) total stator copper section for main winding = 2 * number of turns in the running winding * area of the running winding conductor

c) total stator copper section for main winding = number of turns in the running winding / area of the running winding conductor

d) total stator copper section for main winding = 2* number of turns in the running winding / area of the running winding conductor

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8. What is the formula for the total cross section of rotor bars?

a) total cross section of rotor bars = number of rotor slots * area of each bar

b) total cross section of rotor bars = number of rotor slots / area of each bar

c) total cross section of rotor bars = number of rotor slots + area of each bar

d) total cross section of rotor bars = number of rotor slots – area of each bar

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9. What is the range of the ratio of the total cross section of rotor bars to the total stator copper section for main winding for copper?

a) 0.4-0.8

b) 0.3-0.7

c) 0.5-0.8

d) 0.8-0.9

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10. What is the formula of the end ring current?

a) end ring current = number of rotor slots * bar current * 3.14 * number of poles

b) end ring current = number of rotor slots * bar current * 3.14 / number of poles

c) end ring current = number of rotor slots / bar current * 3.14 * number of poles

d) end ring current = number of rotor slots * bar current / 3.14 * number of poles

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11. What is the range of the ratio of the total cross section of rotor bars to the total stator copper section for main winding for aluminium?

a) 1-1.3

b) 1-1.4

c) 1-1.6

d) 1.2-1.5

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

a) area of each bar = current through each bar / current density through each bar

b) area of each bar = current through each bar * current density through each bar

c) area of each bar = current density through each bar / current through each bar

d) area of each bar = current density through each bar * current through each bar

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13. What is the formula of the area of each end ring?

a) area of each end ring = 0.32 * total cross section of rotor bars * number of poles

b) area of each end ring = 0.32 / total cross section of rotor bars * number of poles

c) area of each end ring = 0.32 * total cross section of rotor bars / number of poles

d) area of each end ring = 1/0.32 * total cross section of rotor bars * number of poles

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14. What is the formula of the rotor teeth flux density?

a) flux density of rotor teeth = maximum flux / (number of rotor slots / number of poles) * length of the teeth * depth of rotor core

b) flux density of rotor teeth = maximum flux * (number of rotor slots / number of poles) * length of the teeth * depth of rotor core

c) flux density of rotor teeth = 1/maximum flux * (number of rotor slots / number of poles) * length of the teeth * depth of rotor core

d) flux density of rotor teeth = maximum flux / (number of rotor slots * number of poles) * length of the teeth * depth of rotor core

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15. What is the range for the ratio of the resistance to reactance in the split phase motors?

a) 0.40-0.55

b) 0.45-0.55

c) 0.45-0.8

d) 0.45-0.6

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## Set 5

1. How many factors does the design of rotor of synchronous machines depend upon?

a) 2

b) 3

c) 4

d) 5

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2. What is the formula for the flux in pole body?

a) flux in pole body = leakage coefficient * useful flux per pole

b) flux in pole body = leakage coefficient / useful flux per pole

c) flux in pole body = leakage coefficient – useful flux per pole

d) flux in pole body = leakage coefficient + useful flux per pole

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3. What is the range of the permissible values of the flux densities in pole body?

a) 1.4-1.7 Wb per m^{2}

b) 1.5-1.7 Wb per m^{2}

c) 1.4-1.6 Wb per m^{2}

d) 1.5-1.6 Wb per m^{2}

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^{2}.The maximum permissible value of the flux density in the pole body is given to be 1.7 Wb per m

^{2}.

4. What is the range of the leakage coefficient in the pole body?

a) 1.1 to 1.2

b) 1.00 to 1.5

c) 1.15 to 1.2

d) 0.75 to 2.3

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5. What is the formula for the area of cross-section of pole body for rectangular poles?

a) area of cross section of pole body = 0.98 * axial length of the pole * breadth of the pole

b) area of cross section of pole body = 0.98 / axial length of the pole * breadth of the pole

c) area of cross section of pole body = 0.98 * axial length of the pole / breadth of the pole

d) area of cross section of pole body = 1/0.98 * axial length of the pole * breadth of the pole

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6. What is the formula for the copper area of the field windings?

a) copper area = full load field mmf * current density in the field winding

b) copper area = full load field mmf / current density in the field winding

c) copper area = full load field mmf + current density in the field winding

d) copper area = full load field mmf – current density in the field winding

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7. What is the formula for the total space required for the winding?

a) total space = copper area + space factor

b) total space = copper area – space factor

c) total space = copper area / space factor

d) total space = copper area * space factor

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8. What is the value of space factor for the strip on edge winding?

a) 0.8-0.9

b) 0.4

c) 0.65

d) 0.75

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9. What is the formula for the height of winding?

a) height of winding = total winding area / depth of winding

b) height of winding = total winding area * depth of winding

c) height of winding = total winding area + depth of winding

d) height of winding = total winding area – depth of winding

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10. What is the formula for the radial length of the pole shoe?

a) radial length of the pole shoe = height of winding – height of pole shoe – 0.02

b) radial length of the pole shoe = height of winding + height of pole shoe – 0.02

c) radial length of the pole shoe = height of winding – height of pole shoe + 0.02

d) radial length of the pole shoe = height of winding + height of pole shoe + 0.02

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11. What is the formula for the height of pole body?

a) height of pole body = height of the winding + 0.02

b) height of pole body = height of the winding * 0.02

c) height of pole body = height of the winding – 0.02

d) height of pole body = height of the winding / 0.02

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12. What is the range of the ratio of radial length of pole to pole pitch?

a) 0.3-1

b) 0.3-1.5

c) 0.7-1

d) 0.7-1.5

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13. The damper windings are made use of in synchronous generators to reduce the oscillations and to prevent hunting?

a) true

b) false

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14. The mmf of the damper windings depends on the pole pitch value?

a) true

b) false

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15. What is the formula for the area per pole of damper pass provided?

a) area per pole of damper pass = 0.2 * specific electric loading * pole pitch * current density in damper bars

b) area per pole of damper pass = 0.2 * specific electric loading * pole pitch / current density in damper bars

c) area per pole of damper pass = 0.2 * specific electric loading – pole pitch / current density in damper bars

d) area per pole of damper pass = 0.2 + specific electric loading * pole pitch / current density in damper bars