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# Multiple choice question for engineering

## Set 1

1. The problem of temperature rise and cooling of transformers is essentially the same as that of rotating machinery?
a) true
b) false

Answer: a [Reason:] There are problems of temperature rise and cooling of transformers which decreases the efficiency of the transformers. The same problems are also seen in the rotating machinery.

2. How are the losses in the transformer and rotating machines converted to?
a) the losses are converted to electrical energy
b) the losses are converted to electrical and mechanical energy
c) the losses are converted to mechanical energy
d) the losses are converted to thermal energy

Answer: d [Reason:] In both the transformer and the rotating machines the losses are converted to thermal energy. This thermal energy causes heating of the transformer parts.

3. In how many ways does heat dissipation occur in transformers?
a) 2
b) 3
c) 4
d) 5

Answer: b [Reason:] The heat dissipation takes place in 3 ways in transformers. They are radiation, convection and conduction.

4. What type of heat dissipation takes place when the heat flows from the outer surface of the transformer part to the oil that cools it?
a) conduction
b) convection
c) conduction and convection

Answer: b [Reason:] When heat flows from the outer surface of transformer part to the oil which cools it, it is convection. In transformers all 3 types of heat dissipation occurs.

5. What type of heat dissipation takes place when heat flows from oil to walls of a cooler?
a) conduction
b) convection
d) conduction and convection

Answer: b [Reason:] When heat flows from oil to walls of the cooler, the heat dissipation type is convection. In transformers all 3 types of heat dissipation takes place.

6. What type of heat dissipation takes place when heat flows from the walls of the cooler to the cooling medium?
a) convection
c) convection and radiation
d) conduction and radiation

Answer: c [Reason:] When the heat flows from the walls of the cooler to the cooling medium, it is both convection and radiation. In transformer all 3 types of heat dissipation occurs.

7. What is the range of the working temperature of oil determined by the tests?
a) 40-600 C
b) 30-600 C
c) 45-600 C
d) 50-600 C

Answer: d [Reason:] The minimum value of the working temperature of oil as cooling medium is determined to be 500C. The maximum value of the working temperature of oil as cooling medium is determined to be 600C.

8. What is the formula for specific heat dissipation due to convection of oil?
a) specific heat dissipation = 40.3*(temperature difference of the surface relative to oil / height of the dissipating surface)1/4 W per m2- 0C
b) specific heat dissipation = 40.3 / (temperature difference of the surface relative to oil / height of the dissipating surface)1/4 W per m2- 0C
c) specific heat dissipation = 40.3*(temperature difference of the surface relative to oil * height of the dissipating surface)1/4 W per m2- 0C
d) specific heat dissipation = 40.3*(temperature difference of the surface relative to oil + height of the dissipating surface)1/4 W per m2- 0C

Answer: a [Reason:] First the temperature difference of the surface relative to oil is calculated, then the height of the dissipating surface is also calculated. Substituting in the above formula provides the specific heat dissipation due to convection of oil.

9. What is the value of specific heat dissipation for convection due to air?
a) 8 W per m2- 0C
b) 6 W per m2- 0C
c) 9 W per m2- 0C
d) 10 W per m2- 0C

Answer: a [Reason:] The value of the specific heat dissipation for convection due to air is 8 W per m2- 0C. The value of specific heat dissipation will vary for different medium.

10. The convection due to air is 10 times the convection due to oil?
a) true
b) false

Answer: b [Reason:] The convection due to oil is 10 times the convection due to air. This constitutes a major valuable property of oil as a cooling medium.

11. How do the walls of the transformer tank dissipate heat?
b) by convection
c) by conduction
d) by convection and radiation

Answer: d [Reason:] The plain walled tanks of the transformer also dissipate heat through convection and radiation. The property is similar to that of the rotating machinery.

12. What is the specific heat dissipated by the plain walled tanks of the transformer by radiation and convection?
a) 6.5, 6 W per m2- 0C
b) 6, 6.5 W per m2- 0C
c) 6.5, 6.5 W per m2- 0C
d) 6, 6 W per m2- 0C

Answer: b [Reason:] The heat dissipated by the plain walled tanks of the transformer by radiation is 6 W per m2- 0C. The heat dissipated by the plain walled tanks of the transformer by convection is 6.5 W per m2- 0C.

13. What is the formula for temperature rise of the transformers?
a) temperature rise = total loss * specific heat dissipation * surface temperature
b) temperature rise = total loss / (specific heat dissipation * surface temperature)
c) temperature rise = total loss / specific heat dissipation / surface temperature
d) temperature rise = total loss * specific heat dissipation / surface temperature

Answer: b [Reason:] Firstly the surface temperature is calculated along with the specific heat dissipation which is nothing but 12.5. Then the losses are calculated and substituted in the above formula.

14. Can the plain walled tanks accommodate the transformer for both large and small outputs?
a) the plain walled tanks can accommodate for large outputs but cannot accommodate for small outputs
b) the plain walled tanks can accommodate for large outputs and small outputs
c) the plain walled tanks cannot accommodate for large outputs and small outputs
d) the plain walled tanks can accommodate for small outputs but cannot accommodate for large outputs

Answer: d [Reason:] The plain walled tanks are large enough to accommodate the transformer and oil has sufficient surface to keep the temperature rise within limits for small outputs. But the plain walled tanks cannot accommodate the transformers for large outputs.

15. How are the ratings of the transformer, losses and temperature rise related?
a) increase, decrease, increase
b) decrease, increase, increase
c) increase, increase, increase
d) decrease, increase, decrease

Answer: c [Reason:] As the rating of the transformer increases, the losses also increase. As the losses increase the heat dissipated increases and gives high temperature rise.

## Set 2

1. What is the function of the motor starter with respect to current?
a) to slow the low current flow
b) to prevent the low current flow
c) to allow the large current flow
d) to prevent the large current flow

Answer: d [Reason:] There are varied type of starters which vary among themselves according to the function. The main function is to prevent the excessive current at the starting.

2. What is the work of the starter with respect to the mechanical stress?
a) to allow large mechanical stress
b) to restrict large mechanical stress
c) to allow small mechanical stress
d) to restrict small mechanical stress

Answer: b [Reason:] The main function of the starter is to prevent the excessive current at the starting. The other work of the starter is to restrict the large mechanical stress from acting on the machines.

3. What is the relation of the current with the starting torque in the starter concept?
a) the starter should restrict current to prevent low starting torque
b) the starter should restrict current to produce high starting torque
c) the starter should send current to prevent low starting torque
d) the starter should send current to produce high starting torque

Answer: d [Reason:] The main function of the starter is to prevent the excessive current flow. At the same time it should allow current to produce good or high starting torque.

4.When does the starter take up liquid rheostat?
a) when the resistance can be varied heavily
b) when the resistance can be varied gradually
c) when the resistance cannot be varied
d) when the resistance should not be varied

Answer: b [Reason:] The starter actually picks up either liquid rheostat or metallic resistance during its operation. The starter takes up liquid rheostat during the situation where the resistance is gradually varied.

5. The starter take up metallic resistance when the resistance should not be varied in steps ?
a) true
b) false

Answer: b [Reason:] The starter actually picks up either liquid rheostat or metallic resistance during its operation. The starter takes up metallic resistance when the resistance is to be varied in steps.

6. What happens when the starter takes up metallic resistance?
a) voltage fluctuates from high to low
b) voltage fluctuates between fixed upper and lower limits
c) current fluctuates from high to low
d) current fluctuates between fixed upper and lower limits

Answer: d [Reason:] The starter actually picks up either liquid rheostat or metallic resistance during its operation. The starter takes up metallic resistance when the resistance is to be varied in steps. When taken with resistance steps, the current fluctuated between upper and lower limits.

7. What is the product of the ratio of the current and the useful flux per pole?
a) product of ratio of current and useful per pole = (useful flux per pole due to upper limit current * upper limit current) / (useful flux per pole due to lower limit current * lower limit current)
b) product of ratio of current and useful per pole = (useful flux per pole due to upper limit current + upper limit current) / (useful flux per pole due to lower limit current + lower limit current)
c) product of ratio of current and useful per pole = (useful flux per pole due to upper limit current – upper limit current) / (useful flux per pole due to lower limit current – lower limit current)
d) product of ratio of current and useful per pole = (useful flux per pole due to upper limit current * lower limit current) / (useful flux per pole due to lower limit current * upper limit current)

Answer: d [Reason:] First the product of useful flux per pole due to upper limit current and lower limit current and then the product of useful flux per pole due to lower limit current and upper limit current. On substitution the product of ratio of current and useful per pole is obtained.

8. How many machines are considered in the calculation of the resistance steps?
a) 2
b) 3
c) 4
d) 5

Answer: b [Reason:] There are 3 machines considered in the calculation of the resistance steps. They are starters for dc shunt motors, starters for dc series motors, starters for three phase slip ring induction motor.

9. What is the concept of notching operation?
a) process of decreasing the voltage
b) process of increasing the efficiency
c) process of cutting out the resistance
d) process of adding on the resistance

Answer: c [Reason:] The process of notching operation occurs In the dc shunt motors. The concept of notching operation means the cutting out the resistance.

10. What happens in the dc shunt motor when the notching process occurs?
a) flux remains constant
b) speed remains constant
c) voltage remains constant
d) current remains constant

Answer: b [Reason:] Notching operation means cutting out the resistance. During the process of notching speed remains constant.

11. What is the formula of the ratio of the lower limit to upper limit of current with respect to the resistance?
a) lower limit of current / upper limit of current = motor resistance / resistance to limit the starting current
b) lower limit of current / upper limit of current = (motor resistance / resistance to limit the starting current)1/number of resistance
c) lower limit of current / upper limit of current = (motor resistance * resistance to limit the starting current)1/number of resistance
d) lower limit of current / upper limit of current = motor resistance * resistance to limit the starting current

Answer: b [Reason:] The motor resistance, resistance to limit the starting current and number of resistance is calculated. On substitution the ratio of lower limit to upper limit of current is obtained.

12. What is the relation of the ratio of rotor current limits and the ratio of lower limit to upper limit current?
a) ratio of rotor current limits = ratio of lower limit to upper limit current
b) ratio of rotor current limits > ratio of lower limit to upper limit current
c) ratio of rotor current limits < ratio of lower limit to upper limit current
d) no relation between ratio of rotor current limits and ratio of lower limit to upper limit current

Answer: a [Reason:] The ratio of rotor current limits and the ratio of lower limit to upper limit current are first calculated. The ratio of rotor current limits is approximately equal to the ratio of lower limit to upper limit current.

13. How many machines are considered for the design of field regulators for dc machines?
a) 2
b) 3
c) 4
d) 5

Answer: a [Reason:] Two machines are considered for the design of field regulators for dc machines. They are the shunt generators and shunt motor.

14. What is the first step in the design of the field regulators for dc machines?
a) calculation of the resistance of section
b) calculation of the total field circuit resistance
c) calculation of the field circuit resistance
d) resistance to be inserted

Answer: b [Reason:] 2 machines are considered in the design of field regulators for dc machines. They are the shunt generators and shunt motor. The first step is the calculation of the field circuit resistance.

15. What is the second step in the design of the field regulators for dc machines?
a) calculation of the resistance of section
b) calculation of the total field circuit resistance
c) calculation of the field circuit resistance
d) resistance to be inserted

Answer: d [Reason:] 2 machines are considered in the design of field regulators for dc machines. They are the shunt generators and shunt motor. The second step is the calculation of the resistance to be inserted.

16. What is the last step involved in the design of field regulators for shunt generators?
a) calculation of the resistance of section
b) calculation of the total field circuit resistance
c) calculation of resistance of section
d) resistance to be inserted

Answer: c [Reason:] 2 machines are considered in the design of field regulators for dc machines. They are the shunt generators and shunt motor. The last step is the calculation of resistance of section.

17. What is the first step in the design of the field regulators for dc motor?
a) number of sections
b) shunt field circuit resistance
c) shunt field resistance
d) resistance of step

Answer: a [Reason:] 2 machines are considered in the design of field regulators for dc machines. They are the shunt generators and shunt motor. The first step is the calculation of number of sections.

18. What is the plot of the magnetization curve?
a) field current in the y axis vs voltage in x axis
b) field current in the x axis vs voltage in y axis
c) armature current in the y axis vs voltage in x axis
d) armature current in the x axis vs voltage in y axis

Answer: b [Reason:] The magnetization curve is the curve which is used to obtain the various values required in the design of field regulators. The curve is the plot of field current in x axis and voltage in y axis.

## Set 3

1. What is the use of the turns compensation in current transformer?
a) to increases the ratio error
b) to reduce the ratio error
c) to increase the phase angle error
d) to reduce the phase angle error

Answer: b [Reason:] There are 2 types of errors in the current transformer. The turns compensation is used to reduce the ratio error.

2.What is the formula of the actual ratio?
a) actual ratio = turns ratio + load current * secondary current
b) actual ratio = turns ratio * load current * secondary current
c) actual ratio = turns ratio + load current / secondary current
d) actual ratio = turns ratio / load current * secondary current

Answer: c [Reason:] The turns ratio is first calculated. Next the load current and secondary current is calculated and on substitution gives the actual ratio.

3. What happens if the number of secondary turns is reduced?
a) the primary turns is reduced
b) the output is reduced
c) the efficiency is reduced
d) the transformation ratio is reduced

Answer: d [Reason:] The reduction of the number of secondary turns reduces the transformation ratio. If the number of secondary turns reduces by 1 percent the actual transformation ratio reduces by equal percentage.

4.What is the best number of secondary turns of the current transformer?
a) 1
b) 2
c) 1 or 2 less than the number such that the turns ratio is equal to the nominal current ratio
d) 1 or 2 more than the number such that the turns ratio is equal to the nominal current ratio

Answer: c [Reason:] The best number of secondary turns of the current transformer is 1 or 2 less than the number such that the turns ratio is equal to the nominal current ratio. For example in a 1000/5 current transformer, the secondary turns number would be 198 or 199 rather than 200.

5. The phase angle error is significantly affected by the small change in secondary turns?
a) true
b) false

Answer: b [Reason:] There are 2 types of errors which is the ratio error and phase angle error. The phase angle error is not significantly effected by a small change in secondary turns.

6. What is the dimension of the round copper wire made use of in the windings of current transformer?
a) 3 cm2
b) 3 mm2
c) 3 m2
d) 3 cm

Answer: b [Reason:] Copper strip is used for primary windings. The dimension of the round copper wire made use of in the windings of current transformer is 3 mm2.

7. What is the range of current density in the windings of the current transformer?
a) 1-3 A per mm2
b) 2-3 A per mm2
c) 1-2 A per mm2
d) 0.5-2 A per mm2

Answer: c [Reason:] The minimum value of the current density in the windings I A per mm2. The maximum value of the current density is 2 A per mm2.

8. How many factors are present in the behavior of transformer under short circuit conditions?
a) 2
b) 3
c) 4
d) 5

Answer: b [Reason:] There are 3 factors present in the behavior of the transformer under short circuit conditions. They are temperature rise, current density, mechanical forces.

## Set 4

1. How many types of electromagnets are present?
a) 2
b) 3
c) 4
d) 5

Answer: a [Reason:] There are 2 types of electromagnets present. They are i) Tractive type and ii) Portative type.

2. What is the other name of the Tractive electromagnet and what is the means of movement of the armature?
a) solenoidal, electrical movement
b) solenoidal, mechanical movement
c) traction, electrical movement
d) traction, mechanical movement

Answer: b [Reason:] The other name for the tractive electromagnet is solenoids. They are designed to produce mechanical .

3. What is the supply given to the tractive electromagnets?
a) only dc supply
b) only ac supply
c) ac and dc supply
d) ac or dc supply

Answer: d [Reason:] The other name for the tractive electromagnet is solenoids. The tractive electromagnets are operated either from ac or dc supply.

4. Among the following what are the applications of the tractive electromagents?
a) track switches
b) electric bells
c) buzzers
d) track switches, bells,buzzers

Answer: d [Reason:] The tractive electromagnets have a large number of application. They are made use of in the track switches, electric bells and buzzers.

5. How does the portative electromagnet work as?
a) holding magnet
b) connecting magnet
c) repulsion magnets
d) attraction magnets

Answer: a [Reason:] The second type of the electromagnets is the portative electromagnet. They usually function as holding magnet.

6. What type of supply is being provided to the portative electromagnet?
a) only ac supply
b) only dc supply
c) ac and dc supply
d) ac or dc supply

Answer: b [Reason:] Portative electromagnets are one type of electromagnet, which function as holding magnet. They operated usually from dc supply only.

7. How many most commonly used electromagnets are present?
a) 2
b) 3
c) 4
d) 5

Answer: b [Reason:] There are 3 most commonly used electromagnets are present. They are I) Flat-faced armature type, II) Horse shoe type, III) Flat-faced plunger type.

8. What type of magnet is made use of to produce large force through a relatively small distance?
a) flat-faced armature type
b) horse shoe type
c) flat-faced plunger type
d) flat-faced plunger type and horse shoe type

Answer: a [Reason:] There are 3 types of most commonly used electromagnets. The flat faced armature type electromagnet is made use of to produce large force through a relatively small distance

9. What material is the flat faced armature type made of?
a) hard steel
b) cast steel
c) cast iron
d) soft steel

Answer: b [Reason:] The flat faced armature type is made up of cast steel. It is used for lifting scrap iron, sheet iron and iron castings.

10. How are the air gaps arranged in the flat faced armature type?
a) magnetic in series and mechanical in parallel
b) magnetic in series and parallel
c) mechanical in series and parallel
d) magnetic in parallel and mechanical in series

Answer: a [Reason:] The flat faced armature types have 2 air gaps within them. They are magnetic in series and are mechanical in parallel and hence produce a holding surface of large effective area.

11. Which among the following are the application of portative electromagnets?
a) lifting magnets
b) magnetic clutches
c) magnetic chucks
d) lifting magnets, magnetic clutches, magnetic chucks

Answer: d [Reason:] The portative electromagnets generally function as holding magnets. The lifting magnets, magnetic chucks, magnetic clutches are all applications of portative electromagnets.

12.What is the relation between force and the air gap length in the flat-faced armature type?
a) force is directly proportional to the air gap length
b) force is indirectly proportional to the air gap length
c) force is directly proportional to the square of the air gap length
d) force is indirectly proportional to the square of the air gap length

Answer: c [Reason:] The force is directly proportional to the square of the air gap length. This condition exists under ideal conditions wherein the effects of saturation and magnetic leakage are negligible.

13. Horse shoe is usually employed for the small magnets?
a) true
b) false

Answer: a [Reason:] The horse shoe is usually employed for the small magnets. It is because of the mechanical adaptability and the ease with which it can be constructed.

14. How many air gaps are present in the flat-faced plunger type?
a) 1
b) 2
c) 3
d) 4

Answer: a [Reason:] The magnetic circuit in the flat faced plunger type is usually short and heavy. It has only one air gap present.

15. What is the relation of the force and the air gap length in the flat faced plunger type?
a) force is directly proportional to the air gap length
b) force is indirectly proportional to the air gap length
c) force is directly proportional to the square of the air gap length
d) force is indirectly proportional to the square of the air gap length

Answer: c [Reason:] Force is directly proportional to the square of the air gap length. The characteristics is similar to that of the flat-faced armature type.

## Set 5

1. What is the special feature of single phase induction motor?
a) high starting torque
b) low starting torque
c) average starting torque
d) zero starting torque

Answer: d [Reason:] The single phase induction motor has no inherent starting torque. Thus special means should be used to make it self starting.

2. How many methods are present in the self starting of the single phase induction motor?
a) 1
b) 2
c) 3
d) 4

Answer: c [Reason:] There are 3 methods involved in the self starting of the single phase induction motor. They are split phase starting, shaded pole starting, repulsion motor starting.

3. What are the names of the windings used in the split phase starting?
a) starting windings
b) auxiliary windings
c) starting or auxiliary windings
d) starting and auxiliary windings

Answer: c [Reason:] The single phase induction motor is not self starting. The starting or auxiliary windings are used along with the running or main windings.

4.What is the displacement of the running and the starting windings used?
a) running winding displaces the starting winding by 1800
b) running winding displaces the starting winding by 900
c) starting winding displaces the running winding by 900
d) starting winding displaces the running winding by 1800

Answer: b [Reason:] The split phase starting makes use of the starting windings along with the running windings. The running winding displaces the starting windings by 900.

5. How is the required phase displacement between the current in the running and starting windings obtained?
a) by connecting a suitable resistor
b) by connecting a suitable capacitor
c) by connecting a suitable inductor
d) by connecting a suitable impedance

Answer: d [Reason:] The running winding displaces the starting winding by 900. The required phase displacement is obtained by connecting a suitable impedance in series with any of the windings.

6. When is the starting winding cut out of the circuit in the split phase motor?
a) when the motor speed reaches 65 % of the full load speed
b) when the motor speed reaches 75 % of the full load speed
c) when the motor speed reaches 50 % of the full load speed
d) when the motor speed reaches 85 % of the full load speed

Answer: b [Reason:] The single phase induction motor is not a self starting machine and hence starting windings are connected in series with the running winding. The starting windings are cut out when the motor speed reaches 75 % of the full load speed.

7. What is the shaded pole starting method?
a) part of the pole is shaded by open circuited copper ring
b) part of the pole is shaded by short circuited copper ring
c) the pole is shaded by open circuited copper ring
d) the pole is shaded by short circuited copper ring

Answer: b [Reason:] One of the starting methods of the single phase induction motor is the shaded pole starting method. Here the part of the pole is shaded by the short circuited copper ring.

8. What happens in the shaded pole starting method according to the displacement?
a) displacement between shaded and unshaded portion varies between 200-250
b) displacement between shaded and unshaded portion varies between 200-350
c) displacement between shaded and unshaded portion varies between 200-300
d) displacement between shaded and unshaded portion varies between 300-450

Answer: c [Reason:] The shaded pole starting method is that the part of the pole is shaded by short circuited copper ring. The displacement between shaded and unshaded portion varies between 200-300.

9. For what type of machines is the shaded pole starting method suitable?
a) for outputs below 60 watt
b) for output below 50 watt
c) for output below 40 watt
d) for output above 50 watt

Answer: a [Reason:] The efficiency of the shaded pole starting method is very low. The shaded pole starting method is used for outputs below 60 watt.

10. When is the repulsion motor starting method used?
a) when low starting torque is required
b) when high starting torque is required
c) when high running torque is required
d) when low running torque is required

Answer: b [Reason:] The repulsion motor starting method is one of the 3 methods of starting the single phase induction motor. It is used when the high starting torque is required.

11. What is the speciality in the repulsion motor starting method?
a) cage winding is replaced by armature windings
b) cage winding is replaced by field windings
c) cage winding is replaced by commutator windings
d) cage winding is replaced by bearings

Answer: c [Reason:] The repulsion motor starting method is one of the methods used in the starting of the single phase induction motor. Here the cage winding is replaced by the commutator windings.

12. What happens in the repulsion motor starting method?
a) the cage windings is dominant
b) the commutator windings are dominant
c) the rotor windings are dominant
d) the stator windings are dominant

Answer: b [Reason:] The repulsion motor starting method is one of the starting methods of single phase induction motor. The commutator windings are dominant and hence gives good starting torque.

13. What is the range of output watt for the shaded pole induction machine?
a) 0.37-50
b) 90-750
c) 90-3700
d) 7.5-370

Answer: a [Reason:] The range of output watt for capacitor type induction motor is 90-750 and that of the repulsion start motor is 90-3700. The range of output watt for resistor type induction motor is 7.5-370 and that of the shaded pole type is 0.37-50.

14. What is the range of the starting current of capacitor type induction motor?
a) 5-7
b) 4–6
c) 2-6
d) 2-3