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Multiple choice question for engineering

Set 1

1. How many factors are present in the relation between rating and dimension of rotating machines?
a) 6
b) 7
c) 8
d) 9

View Answer

Answer: c [Reason:] There are 8 factors present in the relation between rating and dimension of rotating machines. They are symbols, main dimensions, total loadings, specific loadings, output equation, factors affecting size of rotating machine, choice of specific magnetic loading, choice of specific electric loading.

2. What is the formula of the total magnetic loading?
a) total magnetic loading = total flux around the armature periphery at the air gap
b) total magnetic loading = total number of ampere conductors around the armature for periphery
c) total magnetic loading = number of poles/armature total flux
d) total magnetic loading = total flux/number of poles

View Answer

Answer: a [Reason:] There are 2 types of loadings in the total loadings which are total magnetic loading and total electric loading. The total magnetic loading is the total flux around the armature periphery at the air gap.

3. What is the formula of the specific electric loading?
a) specific electric loading = total armature ampere conductors * armature periphery at air gap
b) specific electric loading = total flux around the air gap / area of flux path at the air gap
c) specific electric loading = total armature ampere conductors / armature periphery at air gap
d) specific electric loading = total flux around the air gap * area of flux path at the air gap

View Answer

Answer: c [Reason:] The total flux around the air gap and the area of flux path at the air gap is calculated. On substitution the specific electric loading is calculated.

4. How many terms can be used to express the output of a machine?
a) 3
b) 4
c) 5
d) 6

View Answer

Answer: b [Reason:] There are 4 terms that can be used to express the output of a machine. They are main dimension, specific magnetic loading, specific electric loading, speed.

5. How many factors affecting the size of rotating machines?
a) 3
b) 4
c) 5
d) 2

View Answer

Answer: d [Reason:] There are 2 factors which affect the size of rotating machines. They are speed of the machines and the output coefficient of the machines.

6. How many factors are used to determine the specific magnetic loading?
a) 2
b) 3
c) 4
d) 5

View Answer

Answer: b [Reason:] There are 3 factors are used to determine the specific magnetic loading. They are maximum flux density in iron parts of machine, magnetizing current and core losses.

7. How many factors are used to determine the specific electric loading?
a) 2
b) 3
c) 4
d) 5

View Answer

Answer: c [Reason:] There are 4 factors used to determine the specific electric loading. They are temperature rise, cooling coefficient, size of machine, current density.

8. What is the relation between the output and the flux density?
a) flux density is directly proportional to the output
b) flux density is indirectly proportional to the output
c) flux density is directly proportional to the square of the output
d) flux density is indirectly proportional to the square of the output

View Answer

Answer: a [Reason:] Flux density is one of the factors used in the determination of the specific magnetic loading. The flux density is directly proportional to the output.

9. What is the relation between output and the specific electric loading?
a) specific electric loading is directly proportional to the output
b) specific electric loading is indirectly proportional to the output
c) specific electric loading is directly proportional to the square of the output
d) specific electric loading is indirectly proportional to the square of the output

View Answer

Answer: a [Reason:] The choice of specific electric loading is one of the factors under the relation between rating and dimensions of rotating machines. The specific electric loading is directly proportional to the output.

10. What is the relation of the specific electric loading and the diameter?
a) specific electric loading is directly proportional to the diameter
b) specific electric loading is indirectly proportional to the diameter
c) specific electric loading is directly proportional to the square of the diameter
d) specific electric loading is indirectly proportional to the square of the diameter

View Answer

Answer: b [Reason:] The specific electric loading is one of the factors under the relation between rating and dimension of rotating machines. The specific electric loading is indirectly proportional to the diameter.

11. What is the formula of the I2R loss?
a) I2R loss = number of conductors / copper loss in each conductor
b) I2R loss = number of conductors + copper loss in each conductor
c) I2R loss = number of conductors – copper loss in each conductor
d) I2R loss = number of conductors * copper loss in each conductor

View Answer

Answer: d [Reason:] The number of conductors and copper loss in each conductor is first calculated. On substitution the I2R loss is obtained.

12. What is the formula of the efficiency of the machine?
a) efficiency = output / output + losses
b) efficiency = output * output + losses
c) efficiency = output – output + losses
d) efficiency = output + output + losses

View Answer

Answer: a [Reason:] The output is first calculated from the running of the machine and the different losses are calculated. On substitution the efficiency of the machine is calculated.

13. The fractional horsepower motors have efficiency of order of 98%?
a) true
b) false

View Answer

Answer: b [Reason:] The fractional horse power motors have efficiency of order of 60% or less. The large turbo-alternators have efficiency of order of 98% because efficiency increases with increase in dimensions.

Set 2

1. How is the flux distributed in the field form?
a) to reduce the high voltage
b) to reduce the high current
c) to reduce the harmonics
d) to keep the total reluctance low

View Answer

Answer: d [Reason:] The flux in passing from poles into the armature, does not confine itself over the pole arc but spreads out over the entire pole pitch. The flux will distribute itself in the air gap in such a way that the total reluctance is minimum.

2. What does the flux distribution curve determine in the ac machine?
a) waveshape of voltage
b) waveshape of current
c) waveshape of power
d) commutation conditions

View Answer

Answer: a [Reason:] The flux distribution curve in the ac machine determines the waveshape of the voltage. In dc machine the flux distribution curve determines the commutation conditions.

3. How many techniques are used to plot the field form in salient pole machines?
a) 2
b) 3
c) 4
d) 5

View Answer

Answer: a [Reason:] There are 2 techniques which are used to plot the field form in salient pole machines. They are carter’s fringe curves and the flux plotting by method of curvilinear squares.

4. What is the formula of the flux density in the gap at a distance ‘x’ from the centre of the pole?
a) flux density in the gap at a distance ‘x’ from the centre of the pole = length of air gap at the centre of pole * length of air gap at a distance ‘x’ from the centre of the pole * maximum flux density in air gap
b) flux density in the gap at a distance ‘x’ from the centre of the pole = length of air gap at the centre of pole / length of air gap at a distance ‘x’ from the centre of the pole * maximum flux density in air gap
c) flux density in the gap at a distance ‘x’ from the centre of the pole = length of air gap at the centre of pole * length of air gap at a distance ‘x’ from the centre of the pole / maximum flux density in air gap
d) flux density in the gap at a distance ‘x’ from the centre of the pole = 1/ length of air gap at the centre of pole * length of air gap at a distance ‘x’ from the centre of the pole * maximum flux density in air gap

View Answer

Answer: b [Reason:] The length of air gap at the centre of pole, the length of air gap at a distance ‘x’ from the centre of the pole and the maximum flux density in air gap is calculated. On substitution the flux density in the gap at a distance ‘x’ from the centre of the pole.

5. The plot between carter’s coefficient and the relative flux density is the carter’s fringe curve?
a) true
b) false

View Answer

Answer: a [Reason:] Carter’s fringe curves is one of the techniques used in the plotting of the field form in the salient pole machines. The plot between carter’s coefficient and the relative flux density is called as carter’s fringe curve.

6. What Is the formula of the permeance of the flux tube considering unit depth in the flux plotting technique?
a) permeance of the flux tube = permeability in the air * mean width of flux tube * mean length of flux tube
b) permeance of the flux tube = permeability in the air / mean width of flux tube * mean length of flux tube
c) permeance of the flux tube = permeability in the air * mean width of flux tube / mean length of flux tube
d) permeance of the flux tube =1/ permeability in the air * mean width of flux tube * mean length of flux tube

View Answer

Answer: c [Reason:] The permeability in the air, mean width of the flux tube and the mean length of flux tube is calculated first. On substitution the permeance of the flux tube is obtained.

7. How many rules are to be followed while the flux plotting by method of curvilinear squares?
a) 2
b) 3
c) 4
d) 5

View Answer

Answer: b [Reason:] The flux lines leave and enter from surfaces, bounding the gap, at right angles if it is assumed that iron has infinite permeability as compared with air and then the flux and equipotential lines intersect at right angles. The flux and the equipotential lines are so drawn that each flux is divided into equal number of curvilinear squares.

8. How many factors does the flux distribution in the rotating machines depend on?
a) 2
b) 3
c) 4
d) 5

View Answer

Answer: b [Reason:] The flux distribution in the rotating machines depends upon 3 factors. They are shape of pole, the distribution of field windings and the load condition.

9. How should the flux distribution be in the case of ac machines?
a) sinusoidal
b) rectangular
c) square
d) circular

View Answer

Answer: a [Reason:] The flux distribution in the case of ac machines should be sinusoidal. The flux distribution in the case of dc machines should be rectangular.

10. How should the air gap and the fringing effects be if the field form of a salient pole machine is rectangular?
a) air gap under the pole arc is not constant, fringing effects are considered
b) air gap under the pole arc is constant, fringing effects are considered
c) air gap under the pole arc is constant, fringing effects are not considered
d) air gap under the pole arc is not constant, fringing effects are not considered

View Answer

Answer: c [Reason:] The field form of a salient pole machine is rectangular if the air gap under the pole arc is not constant. The field form of a salient pole machine is rectangular if the fringing effects are not considered.

11. What series is used to analyze the field form?
a) z-series
b) fourier series
c) fourier transform
d) z-transform

View Answer

Answer: b [Reason:] The field form of a salient pole is rectangular is the air gap under pole arc is uniform and if fringing effects are neglected. The field form can be analyzed for its harmonic contents with the help of Fourier series.

12. What happens if the field form is symmetrical about the pole axis?
a) north and south pole of a machine are similar
b) no harmonics
c) no cosine terms
d) north and south pole of a machine are similar, no harmonics, no cosine terms

View Answer

Answer: d [Reason:] If the field form is symmetrical about the pole axis the north and south pole of a machine are similar. As the poles are similar, no harmonics and no cosine terms and the constant term is zero.

13. What Is the formula for the amplitude of the fundamental curve?
a) amplitude of the fundamental curve = 1.27 * flux density in the air gap * cosine (phase angle/2)
b) amplitude of the fundamental curve = 1.27 / flux density in the air gap * cosine (phase angle/2)
c) amplitude of the fundamental curve = 1.27 * flux density in the air gap / cosine (phase angle/2)
d) amplitude of the fundamental curve = 1/1.27 * flux density in the air gap * cosine (phase angle/2)

View Answer

Answer: a [Reason:] The flux density in the air gap is calculated along with the cosine of the phase angle divided by 2. On substitution the amplitude of the fundamental curve is calculated.

Set 3

1. How many factors are present in the operating characteristics?
a) 2
b) 3
c) 4
d) 5

View Answer

Answer: c [Reason:] There are 4 operating characteristics present in the single phase induction motor. They are mmf for air gap, saturation factor, iron loss, friction and windage loss.

2. How many parts does the stator mmf passes through?
a) 3
b) 4
c) 5
d) 6

View Answer

Answer: c [Reason:] The stator mmf produced in the motor passes through 5 parts. They are air gap, stator teeth, stator core, rotor teeth, rotor core.

3. What is the angle at which the value of the flux density should be for the calculation of mmf?
a) 400
b) 600
c) 800
d) 700

View Answer

Answer: b [Reason:] The calculation of mmf should be based upon the value of the flux density. The value of flux density at 600 from the interpolar axis as far as gap and teeth are concerned.

4.What is the value of the flux density with respect to average flux density?
a) value of flux density = 1.67 times of average flux density
b) value of flux density = 1.70 times of average flux density
c) value of flux density = 1.60 times of average flux density
d) value of flux density = 1.50 times of average flux density

View Answer

Answer: a [Reason:] The value of flux density at 600 from the interpolar axis as far as gap and teeth are used in the calculation of mmf. The value of flux density = 1.67 times of average flux density.

5. What is the formula for the mmf required for air gap?
a) mmf required for air gap = 8,00,000 * air gap flux density * air gap constant / air gap length
b) mmf required for air gap = 8,00,000 * air gap flux density * air gap constant * air gap length
c) mmf required for air gap = 8,00,000 * air gap flux density / air gap constant * air gap length
d) mmf required for air gap = 8,00,000 / air gap flux density * air gap constant * air gap length

View Answer

Answer: b [Reason:] The air gap flux density, air gap constant, air gap length are calculated first. On substitution the mmf required for air gap can be obtained.

6. What is the formula for the saturation factor?
a) saturation factor = total mmf required for the magnetic circuit/mmf required for air gap
b) saturation factor = total mmf required for the magnetic circuit + mmf required for air gap
c) saturation factor = total mmf required for the magnetic circuit – mmf required for air gap
d) saturation factor = total mmf required for the magnetic circuit * mmf required for air gap

View Answer

Answer: a [Reason:] The total mmf required for the magnetic circuit and the mmf required for air gap is calculated. On substitution the saturation factor is obtained.

7. What is the range of the saturation factor in the single phase induction motor?
a) 1.1-1.3
b) 1.0-1.2
c) 1.1-1.35
d) 1.2-1.6

View Answer

Answer: c [Reason:] The minimum value of the saturation factor in the single phase induction motor is 1.1. The maximum value of the saturation factor in the single phase induction motor is 1.35.

8. What is the relation between flux densities with respect to saturation factor?
a) flux density is indirectly proportional to the square of the saturation factor
b) flux density is directly proportional to the square of the saturation factor
c) flux density is indirectly proportional to the saturation factor
d) flux density is directly proportional to the saturation factor

View Answer

Answer: d [Reason:] The saturation factor is kept low if the flux densities in the teeth and core are low. The saturation factor is kept high if the flux densities in the teeth and core are high.

9. What factors are considered while calculating iron loss in stator teeth and core?
a) flux densities
b) weights
c) flux densities or weights
d) flux densities and weights

View Answer

Answer: d [Reason:] The iron loss in stator teeth and core are found by calculating their flux densities. The iron loss in stator teeth and core are found by calculating their weights.

10. What is the relation between total iron loss for induction motors and the sum of stator tooth and core loss?
a) total iron loss for induction motors = 1.3-2.3 times the sum of stator tooth and core loss
b) total iron loss for induction motors = 1.4-2.4 times the sum of stator tooth and core loss
c) total iron loss for induction motors = 1.5-2.5 times the sum of stator tooth and core loss
d) total iron loss for induction motors = 1.3-2 times the sum of stator tooth and core loss

View Answer

Answer: c [Reason:] The total iron loss for induction motors is 1.5-2.5 times the sum of stator tooth and core loss. The total iron loss is due to fundamental frequency flux.

11. What is the range of the multiplying factor when test data is not available?
a) 1.7-2
b) 1.75-2.2
c) 1.6-2.3
d) 1.5-2

View Answer

Answer: b [Reason:] The multiplying factor should be obtained from tests of motors of similar design. When test data is not available, a value of 1.75 to 2 may be used.

12. What are the factors which result in the bearing friction and windage loss?
a) ball bearings
b) sleeve bearing
c) ball bearing and sleeve bearing
d) ball bearing or sleeve bearing

View Answer

Answer: d [Reason:] The bearing friction and windage loss will depend upon the ball bearings. The bearing friction and windage loss will also depend upon the sleeve bearings.

13. What is the friction and windage loss for a 1500 rpm machine?
a) 3-7% of watt output
b) 3-9% of watt output
c) 4-8% of watt output
d) 1-5% of watt output

View Answer

Answer: c [Reason:] The friction and windage loss and a speed of 1500 rpm, it is usually minimum 4% of the watt output. The friction and windage loss and a speed of 1500 rpm, it is usually maximum of 8% of the watt output.

14. The high values actually apply for the small motors below 150 W?
a) true
b) false

View Answer

Answer: b [Reason:] The friction and windage loss and a speed of 1500 rpm, it is usually 4-8% of the watt output. The high values apply to small motors below 180 W.

15. The loss for the sleeve bearing having stator outer diameter 150 mm and 1000 rpm is 3.7 W?
a) true
b) false

View Answer

Answer: a [Reason:] The sleeve bearing having a stator outer diameter of 150 mm has losses at different running speed. The 1000 rpm machine gives loss of 3.7 W.

16. What is the range of the frequency constant?
a) 0.86-1.0
b) 0.82-1.0
c) 0.9-1.0
d) 0.5-1.0

View Answer

Answer: a [Reason:] The minimum value of the frequency constant used in the output equation of P.H Tricky is 0.86. The maximum value of the frequency constant used in the output equation of P.H Tricky is 1.0.

17. What is the range of the motor type constant?
a) 1.1-1.3
b) 1.0-1.4
c) 1.1-1.42
d) 1.1-1.5

View Answer

Answer: c [Reason:] The minimum value of the motor type constants is 1.1. The maximum value of the motor type constants is 1.42.

18. What is the formula of the most economical relation between D and L?
a) length = 0.6 * diameter
b) length = 0.5 / diameter
c) length = 0.6 / diameter
d) length = 0.63 * diameter

View Answer

Answer: d [Reason:] The length and the diameter are the 2 main dimensions of the single phase induction motor. The most economical relation between length and diameter is length = 0.63 * diameter.

Set 4

1. What is the formula of the output equation of ac machines?
a) kVA input Q = output coefficient * diameter2 * length * synchronous speed
b) kVA input Q = output coefficient / diameter2 * length * synchronous speed
c) kVA input Q = output coefficient * diameter2 / length * synchronous speed
d) kVA input Q = output coefficient * diameter2 * length / synchronous speed

View Answer

Answer: a [Reason:] The output coefficient, diameter, length and synchronous speed are first calculated. Then on substitution gives the kVA input and in turn gives the output equation.

2. What is the formula for the output coefficient of the output equation?
a) output coefficient = 11 * winding space factor * specific magnetic loading / specific electric loading * 10-3
b) output coefficient = 11 * winding space factor * specific magnetic loading * specific electric loading * 10-3
c) output coefficient = 11 * winding space factor / specific magnetic loading * specific electric loading * 10-3
d) output coefficient = 11 / winding space factor * specific magnetic loading * specific electric loading * 10-3

View Answer

Answer: b [Reason:] The winding space factor, specific magnetic loading, specific electric loading is calculated. On substitution gives the output coefficient used for the calculation of output equation.

3. What is the formula of the kVA input if the rating of the machine is given in horse power?
a) kVA input = horse power / 0.746 * efficiency * power factor
b) kVA input = horse power * 0.746 * efficiency * power factor
c) kVA input = horse power * 0.746 / efficiency * power factor
d) kVA input = horse power * 0.746 * efficiency / power factor

View Answer

Answer: c [Reason:] The horse power rating of the machine along with the efficiency and power factor is calculated. On substitution the kVA input can be obtained.

4. What is the ratio of the efficiency for 75 watt to 750 watt motor?
a) 4:7
b) 5:7
c) 6:7
d) 3:7

View Answer

Answer: b [Reason:] The efficiency of the 75 watt motor is 50%. The efficiency of the 750 watt motor is 70%.

5. What is the ratio of power factor of the 75 watt to 750 watt motor?
a) 0.55 : 0.60
b) 0.50 : 0.60
c) 0.55 : 0.65
d) 0.50 : 0.65

View Answer

Answer: c [Reason:] The power factor of the 75 watt motor is 0.55. The power factor of 750 watt motor is 0.60.

6. The smaller values are applicable for lower rating machines?
a) true
b) false

View Answer

Answer: a [Reason:] The smaller values are applicable for lower rating machines. The power factor is 0.55 for 75 watt motor and the efficiency is 50% for the 75 watt motor.

7. What is the efficiency for the output watt of 180?
a) 0.38
b) 0.48
c) 0.57
d) 0.65

View Answer

Answer: c [Reason:] The efficiency of the output watt of 37 is 0.38 and the efficiency of output watt of 90 is 0.48. The efficiency of the output watt of 180 is 0.57.

8. What is the power factor of output watt of 90?
a) 0.46
b) 0.51
c) 0.56
d) 0.62

View Answer

Answer: b [Reason:] The power factor of output watt of 37 is 0.46 and the power factor for 180 output watt is 0.56. The power factor of the output watt of 90 is 0.51.

9. What factor does the output coefficient depend upon?
a) specific magnetic loading
b) specific electric loading
c) specific electric loading or specific magnetic loading
d) specific electric loading and specific magnetic loading

View Answer

Answer: b [Reason:] The output coefficient depends upon the specific electric loading. The output coefficient also depends upon the specific magnetic loading.

10. What is the range of the average flux density used in the output equation?
a) 0.30-0.55 weber per m2
b) 0.30-0.50 weber per m2
c) 0.35-0.45 weber per m2
d) 0.35-0.55 weber per m2

View Answer

Answer: d [Reason:] The minimum value of the average flux density is 0.35 weber per m2. The maximum value of the average flux density is 0.55 weber per m2.

Set 5

1. What is the formula for the diameter of the single phase core type transformer?
a) D = diameter of circumscribing circle + Width of window
b) D = diameter of circumscribing circle – Width of window
c) D = diameter of circumscribing circle * Width of window
d) D = diameter of circumscribing circle / Width of window

View Answer

Answer: a [Reason:] First the diameter of the circumscribing circle is obtained. Next, the width of the window is calculated, and the sum of both the data provides the diameter of the single phase core transformer.

2. What is the formula for height of the single phase core type transformer?
a) height = height of the window – height of the yoke
b) height = height of the window + height of the yoke
c) height = height of the window – (2*height of the yoke)
d) height = height of the window + (2*height of the yoke)

View Answer

Answer: d [Reason:] The height of the window is first obtained. Next, the height of the yoke is calculated and it is multiplied by 2. Addition of both the values gives the height of the single phase core type transformer.

3. What is the formula for width of the single phase core type transformer?
a) width = Width of largest stamping / Diameter of the transformer
b) width = Width of largest stamping + Diameter of the transformer
c) width = Width of largest stamping – Diameter of the transformer
d) width = Width of largest stamping * Diameter of the transformer

View Answer

Answer: b [Reason:] Firstly, the width of the largest stamping is calculated. Next, the diameter of the transformer is calculated and the sum of both the values gives the width of the transformer.

4.What is the formula for the width over 2 limbs?
a) width = Width of largest stamping + Diameter of the transformer
b) width = Diameter + outer diameter of hv windings
c) width = Diameter – outer diameter of hv windings
d) width = outer diameter of hv windings

View Answer

Answer: b [Reason:] width = outer diameter of hv windings is the width over one limb. width = Width of largest stamping + Diameter of the transformer is the formula for width of the transformer.

5. The formula for single phase core type and three phase core type diameter and height are same?
a) true
b) false

View Answer

Answer: a [Reason:] D = diameter of circumscribing circle + Width of window is the diameter of single phase and 3 phase core type transformers. height = height of the window + (2*height of the yoke) is the height of the single and three phase core type transformers.

6. What is the formula for the width over one limb?
a) width over one limb = outer diameter of hv winding
b) width over one limb = 2*Diameter – outer diameter of hv winding
c) width over one limb = 2*Diameter + outer diameter of hv winding
d) width over one limb = Diameter + outer diameter of hv winding

View Answer

Answer: a [Reason:] Width over one limb = 2*Diameter + outer diameter of hv winding is the formula for the width over 3 limbs. For one limb the width is equal to the outer diameter of hv winding.

7. What is the formula for the width of the single phase shell type transformer ?
a) width = 2*Width of the window + width of the largest stamping
b) width = Width of the window + 4*width of the largest stamping
c) width = Width of the window + width of the largest stamping
d) width = 2*Width of the window + 4*width of the largest stamping

View Answer

Answer: d [Reason:] First the width of the window is obtained. Next the width of the largest stamping is obtained. Substituting in the above formula provides the width of the single phase shell type transformer.

8. What is the height of the single phase shell type transformer?
a) height = height of window + width of the largest stamping
b) height = 2*height of window + width of the largest stamping
c) height = height of window + 2* width of the largest stamping
d) height = height of window – width of the largest stamping

View Answer

Answer: c [Reason:] First the height of the window is obtained. Then the width of the largest stamping is calculated and substituting in the above formula provides the height of the single phase shell type transformer.

9. What is the formula to calculate the voltage per turn of the transformer?
a) voltage per turn = space factor * square root of output power
b) voltage per turn = space factor / square root of output power
c) voltage per turn = space factor / square root of output power
d) voltage per turn = space factor * 2*square root of output power

View Answer

Answer: a [Reason:] The corresponding space factor is obtained using the formula. Then the output power is obtained and square root of the output power is taken and substituted in the above formula to obtain the voltage per turn.

10. What is the formula for the net cross sectional area of the core of the transformer?
a) cross sectional area = voltage per turn * 4.44 * frequency * magnetic field
b) cross sectional area = voltage per turn / 4.44 * frequency * magnetic field
c) cross sectional area = voltage per turn * 4.44 / frequency * magnetic field
d) cross sectional area = voltage per turn * 4.44 * frequency / magnetic field

View Answer

Answer: b [Reason:] For obtaining the cross sectional area, the voltage per turn is obtained. The frequency is always 50 Hz. Then the magnetic field is obtained and substituted in the above formula.

11. What is the formula for the diameter of the circumscribing circle of the transformer?
a) diameter of the circumscribing circle = 2*square root of ratio of cross sectional area of the core to the space factor
b) diameter of the circumscribing circle = 3*square root of ratio of cross sectional area of the core to the space factor
c) diameter of the circumscribing circle = square root of ratio of cross sectional area of the core to the space factor
d) diameter of the circumscribing circle = 4*square root of ratio of cross sectional area of the core to the space factor

View Answer

Answer: c [Reason:] First the cross sectional area of the core is obtained by the formula cross sectional area = voltage per turn / 4.44 * frequency * magnetic field. Next the space factor is obtained. Substituting in the formula provides the diameter of the circumscribing circle.

12. What is the formula for the width of the window of the transformer?
a) width of the window = distance between core centers + diameter of the circumscribing circle
b) width of the window = distance between core centers – diameter of the circumscribing circle
c) width of the window = distance between core centers * diameter of the circumscribing circle
d) width of the window = distance between core centers / diameter of the circumscribing circle

View Answer

Answer: b [Reason:] The diameter of the circumscribing circle is obtained from the formula, diameter of the circumscribing circle = square root of ratio of cross sectional area of the core to the space factor. After obtaining the distance between core centers, the width of the window is obtained.

13. What is the formula for window area of the transformer?
a) window area = output power * 2.22 * frequency * magnetic field * window space factor * current density * area of cross section of the core *103
b) window area = output power / 2.22 * frequency * magnetic field * window space factor * current density * area of cross section of the core *103
c) window area = output power / 3.33 * frequency * magnetic field * window space factor * current density * area of cross section of the core *103
d) window area = output power * 3.33 * frequency * magnetic field * window space factor * current density * area of cross section of the core*103

View Answer

Answer: b [Reason:] The window space factor, the current density and the core cross sectional area are obtained by their respective formula. The frequency is 50Hz and then the magnetic field and the output power is calculated to obtain the window space factor.

14. What is the formula for the height of the window?
a) height of window = area of window * width of the window
b) height of window = area of window + width of the window
c) height of window = area of window – width of the window
d) height of window = area of window / width of the window

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Answer: d [Reason:] First the area of the window is obtained. Next the window width is obtained. The ratio of both gives the height of the window.

15. The range of the ratio of the height of the window to the width of the window is 2-4?
a) true
b) false

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Answer: a [Reason:] The ratio of the height of the window to the width of the window should be adjusted such that it is above 2. The ratio of the height of the window to the width of the window should be adjusted such that it is below 4.