# Multiple choice question for engineering

## Set 1

1. Hopkinson’s test of D.C. machines is conducted at _______________

a) No-load

b) Part load

c) Full-load

d) Overload

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2. Hopkinson’s test requires ____________

a) One DC machine on which test is carried out

b) Two different DC machines

c) Two identical DC machines

d) Can be worked with one or two machines

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3. In Hopkinson’s test, two machines are connected in ______________

a) Series

b) Parallel

c) Can be connected in parallel or series

d) Two machines are not required

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4. What will happen if field current of generator in Hopkinson’s test is increased?

a) Current through motor armature will increase

b) Current through motor armature will decrease

c) Current through motor armature will remain constant

d) Motor armature current cannot be determined

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5. What will happen if field current of motor in Hopkinson’s test is decreased?

a) Current through motor armature will increase

b) Current through motor armature will decrease

c) Current through motor armature will remain constant

d) Motor armature current can’t be determined

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6. Hopkinson’s test is a regenerative test.

a) True

b) False

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7. For carrying out load test on Hopkinson’s test setup _________________

a) Actual load is needed

b) By changing field currents in two machines load can be changed

c) Can’t carry out

d) By changing the armature current test is carried out

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8. Hopkinson’s test gives _______________

a) Combined iron losses of two machines which can be separated

b) Combined iron losses of two machines which can’t be separated

c) Doesn’t include iron losses

d) Depends on actual setup

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9. Hopkinson’s test is suitable for ______________

a) Small machines only

b) Small and medium machines

c) All machines

d) Only large machines

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10. Why field test is conducted even if Hopkinson’s test is present?

a) Instability of an operation

b) Possibility of run-away speed

c) Both instability and possibility of run-away speed

d) Field test is not conducted

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11. In field’s test generator field and motor field are connected in ______________

a) Series

b) Parallel

c) Alternatively, series and parallel

d) Not connected

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## Set 2

1. Resultant pitch in the lap winding is__________

a) Depends on Y_{b} value

b) Depends on Y_{f} value

c) Depends on Y_{b} and Y_{f} value

d) Always equal to 2

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_{b}and Y

_{f}which is equal to 2, irrespective of Y

_{b}and Y

_{f}value.

2. What is the condition of retrogressive winding?

a) Y_{b} > Y_{f}

b) Y_{b} < Y_{f}

c) Y_{b} = Y_{f}

d) No condition in bterms of Y_{b} and Y_{f}

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_{b}or Y

_{f}. For retrogressive winding Y

_{b}< Y

_{f}.

3. What is the value of Y_{b} for a lap winding with a 4-pole, 12-slot armature with two coil sides/slot. Assume single-turns coils.

a) 3

b) 5

c) 7

d) 9

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_{CS}= 12/4= 3. Y

_{b}= 2

_{YCS}+1= 7.

4. What is the value of Yf for a lap winding with a 4-pole, 12-slot armature with two coil sides/slot? (Assume single-turns coils – progressive winding)

a) 3

b) 5

c) 7

d) 9

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_{CS}= 12/4= 3. Y

_{b}= 2Y

_{CS}+1= 7 Y

_{f}=Y

_{b}– 2= 7-2= 5.

5. Equalizer rings are needed in lap winding.

a) False

b) True

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6. What is the symmetry requirement of lap winding?

a) 2C/P= 0

b) 2C/P= integer

c) 2C/P= non-integer

d) Can’t express mathematically

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7. What is the relation between number of parallel paths(A) and number of poles(P)?

a) A = P

b) A < P

c) A > P

d) No relation exists

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8. Current flowing through the armature conductors Ic is related to total current Ia by_______

a) Ic = A Ia

b) Ic = Ia/A

c) Ic = A^{2} Ia

d) Ic = A/Ia

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9. Value of commutator pitch in lap winding is_____

a) +2

b) +1 or -1

c) -2

d) Different for different parameters

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10. What is the value of Yf for a lap winding with a 4-pole, 12 commutator segments, with two coil sides/slot.?

(Assume single-turns coils -retrogressive winding).

a) 9

b) 3

c) 11

d) 5

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_{CS}= 12/4= 3. Y

_{b}= 2Y

_{CS}+1= 7 Y

_{f}=Y

_{b}+ 2= 7+2= 9.

## Set 3

1. Which DC motor is generally preferred for cranes and hoists?

a) Series motor

b) Shunt motor

c) Cumulatively compounded motor

d) Differentially compounded motor

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2. Which of the following motor has the poorest speed regulation?

a) Shunt motor

b) Series motor

c) Differential compound motor

d) Cumulative compound motor

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3. Buses, trains, trolleys, hoists, cranes make use of DC series motor because __________

a) It provides low starting torque

b) Cost efficient

c) It provides high starting torque

d) It requires minimum power compare to other motors

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4. DC motor is to drive a load which is having certain minimum value for most of the time and some peak value for short duration. We will select the _______

a) Series motor

b) Shunt motor

c) Compound motor

d) Cannot be determined

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5. Which DC motor has got maximum self-relieving property?

a) Series motor

b) Shunt motor

c) Cumulatively compounded motor

d) Differentially compounded motor

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6. Which motor should not be started on no-load?

a) DC Series motor

b) DC Shunt motor

c) Synchronous motor

d) Induction motor

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7. Which of the following is the correct equation for DC series motor ________

a) [ V_{t} / k_{φ}]- [ R_{se} +R_{a} / k_{φ}] I_{a}

b) [ V_{t} / k_{φ}]- [ R_{a}/ kφ2] Ia

c) [ V_{t} / k_{φ}^{2}]- [R_{se} +R_{a}/ k_{φ}^{2}] I_{a}

d) [ V_{t} / k_{φ}^{2}] + [ R_{a}/ k_{φ}^{2}] I_{a}

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_{t}-I

_{a}R

_{a}-I

_{a}R

_{se}) and back emf= kφn. Thus, by combining these equations and by assuming all constants equal to k we get, the final equation shown above.

8. Actual speed obtained at any value of armature current comparing to speed obtained by assuming linear magnetic assumption in DC series motor is _______

a) Same

b) Higher

c) Lower

d) Cannot say

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9. Torque of e DC series motor is __________

a) Directly proportional to armature current

b) Inversely proportional to armature current

c) Directly proportional to square of armature current

d) Inversely proportional to square of armature current

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10. Practically, at higher values of armature current torque does not follow its relationship with armature current.

a) True

b) False

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11. What will happen to a torque, if a DC series motor is accidentally connected to single phase ac supply voltage?

a) Pulsating and unidirectional

b) Steady and unidirectional

c) Oscillating

d) Cannot be determined

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## Set 4

1. Which winding has large number of turns?

a) Shunt field

b) Series field

c) Both have same number of turns

d) Depends on requirement

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2. Which winding contains wire with higher thickness?

a) Shunt field

b) Series field

c) Both have same number of turns

d) Depends on requirement

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3. Which winding have higher resistance?

a) Shunt field

b) Series field

c) Both have same number of turns

d) Depends on requirement

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4. Which is more practical method used in control of series field?

a) Diverter

b) Tappings

c) Switch relay

d) Cannot be determined

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5. In compound excitation, which winding/s is/are excited?

a) Shunt

b) Series

c) Both

d) Cannot be determined

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6. In which type of excitation air gap flux increases with armature current?

a) Differential compound

b) Cumulative compound

c) Differential and Cumulative

d) Cannot be determined

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7. In differential compound excited machine, what is the variation in air gap flux per pole with respect to armature current?

a) Increases

b) Decreases

c) Remains constant

d) Always varies

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8. Which winding in compound excitation is responsible for change in air gap flux per pole?

a) Series

b) Parallel

c) Interconnected

d) No coil is responsible

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9. How short shunt and long shunt compound winding is selected?

a) Mechanical considerations

b) Switch reversal

c) Performance

d) Mechanical considerations and switch reversal

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10. If a DC compound machine connected as a motor is about to use as a generator, we reverse the series field connections.

a) True

b) False

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11. For a long-shunt compound motoring, which of the following equation is correct?

a) V_{t}= E_{a}+ I_{a}(R_{a}+ R_{se})

b) V_{t}= E_{a}– I_{a}(R_{a}+ R_{se})

c) V_{t}= E_{a}+ I_{a}(R_{a}– R_{se})

d) V_{t}= -E_{a}+ I_{a}(R_{a}+ R_{se})

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_{L}is supplied through the terminals which split into I

_{f}and I

_{a}.

12. V_{t}= E_{a}– I_{a}(R_{a}+ R_{se}) is the equation for _______________

a) Short shunt compound motoring mode

b) Short shunt compound generating mode

c) long shunt compound motoring mode

d) Cannot be determined

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_{a}– I

_{f}.

13. How shunt field is controlled?

a) Diverter resistor in parallel

b) Tapped field winding

c) Series regulating resistance

d) Other methods

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14. The generator is called flat compounded if _____________

a) The series field ampere turns are such as to produce the same voltage at rated load as at no load

b) The series field turns are such as that the no load voltage is smaller than the rated load voltage

c) The rated voltage is less than the no load voltage

d) Cannot be determined

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## Set 5

1. In three-point starter, as a starting handle is rotated __________

a) The resistance is added into armature circuit

b) The resistance is removed from field circuit

c) The resistance is added into field circuit

d) Resistance is neither added nor removed

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2. How much torque is ensured by resistance adding arrangement in 3-point starter?

a) Low and non-zero

b) Infinite

c) High finite

d) Zero

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3. The resistance of NVC is _______

a) Small

b) Large

c) Infinite

d) Zero

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4. NVC will release the handle electromagnetically when ________

a) In the case of failure of field current

b) If the resistance is very high

c) At the end of each rotation

d) At the start of each rotation

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5. Over-load coil performs the function when __________

a) In the case of failure of field current

b) If the resistance is very high

c) If armature current increases beyond certain value

d) At the start of each rotation

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6. In 4-point starters the resistance is added in series with NVC because __________________

a) To increase field current

b) To increase armature current

c) To limit the NVC current

d) To limit armature current

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7. What will be the γ value for starter taking 4 steps, where ratio of resistance at maximum allowable current to armature resistance is equal to 1.8?

a) 1.2164

b) 1.8

c) 2.2468

d) 0.8220

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^{n-1}= ratio of resistance at maximum allowable current to the armature resistance. Substituting values for n=4, we get γ=1.2164.

8. Maximum allowable current for a 240-V DC shunt motor is equal to 65 A. Minimum allowable current for same is equal to 40 A. What will be the value of γ?

a) 0.6153

b) 1.265

c) 1.625

d) 2.652

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9. For a certain machine having γ = 1.8, we are using starter with 5 steps. What will be the resistance at step 3 if step 2 resistance is equal to 2 Ω?

a) 2.111

b) 1.111

c) 3.6

d) 10.8

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_{n}/r

_{n-1}. So, for calculating resistance at step 3 we’ll substitute the corresponding values in the equation, which will give step 3 resistance as 1.1111Ω.

10. Which of the following is the correct formula for calculating step resistance?

a) γ = r_{n}/r_{n-1}

b) γ = r_{n}/r_{n+1}

c) γ = r_{n}*r_{n-1}

d) γ = r_{n}*r_{n+1}

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11. Which of the following starter can sufficiently start the DC series motor?

a) 3-point starter

b) 4-point starter

c) 2-point starter

d) Cannot be determined