300 Important DC Motor MCQ Questions & Answers with Explanation | PDF Free Download
1.In a dc machine iron loss are independent of variation in
- AVoltage
- BSpeed
- CLoad
- DBoth a and b
2.In a dc machine, iron losses result in
- AExcessive heating of core
- BLoss of efficiency
- CRise in temperature of ventilating air
- DAll of the above
3.The losses occurring in a dc machine has the largest percentage is
- AIron loss
- BWindage loss
- CCopper loss
- DIron loss
4.Which of the following losses occurring in a dc machine varies significantly with the load?
- AArmature copper loss
- BShunt field copper loss
- CMagnetic or iron losses
- DMechanical losses
5.The armature core of a dc machine gets overheated due to
- ACopper loss occurring in armature windings only
- BEddy current loss only
- CHysteresis loss only
- DAll of the above
6.The overall efficiency of a well-designed dc machine may be expected to be around
- A99%
- B92%
- C75%
- D50%
7.Which of the following motor is expected to have maximum full load efficiency?
- A1 kW
- B5 kW
- C30 kW
- D100 kW
8.Efficiency of a dc machine is maximum when the variable losses are equal to
- AConstant losses
- BSquare of the constant losses
- CSquare root of the constant loses
- DNone of the above
9.The efficiency of a dc machine will be ________when the variable losses are equal to constant losses.
- A100%
- BMaximum
- CMinimum
- D50%
10.DC machines are generally designed for maximum efficiency around
- AFull load
- B75%
- C50%
- D25%
11.In direct method of determination of efficiency of a dc machine
- ACopper losses, magnetic losses and mechanical losses are measured
- BThe machine is actually loaded and input power and output power are measured
- CEither (a) and (b)
- DNone of these
12.The efficiency of a dc machine can be determined without directly loading it with
- AMachine rating
- BArmature and field resistance
- CNo load input of het machine
- DAll of the above information
13.The efficiency of a dc series machine cannot be determined by Swinburne's test as
- AA series motor has very high starting torque
- BA series motor draws excessive current from the supply mains on no load
- CA series motor runs at dangerously high speed on no load
- DAll of the above
14.In Swinburne?s test of a dc machine
- ANo load losses are calculated and copper losses are measured
- BNo load losses are measured and the copper losses are calculated
- CBoth the no load losses and copper losses are calculated
- DBoth the no load losses and the copper losses are measured
15.The test that can be used for determination of no-load losses in a large dc shunt machine is
- ABrake test
- BField test
- CHopkinson?s test
- DSwinburne?s test
16.In Swinburne?s test of determination of efficiency of a dc shunt machine the no load input power supplies
- AArmature and shunt field copper losses
- BIron losses
- CFriction and windage loses
- DAll of the above
17.Performance of large dc machine regarding communication and temperature rise etc. at full load can be checked by ____test
- ABrake
- BSwinburne?s
- CHopkinson?s
- DRunning down
18.In the Kapp?s modification of Hopkinson?s test for dc machines
- AThe power losses in the two machines are supplied electrically
- BThe power losses in the two machines are supplied mechanically
- CThe two machines are not coupled mechanically
- DNone of the above
19.The main disadvantage of Hopkinson's test is that
- AIt needs large power
- BIt needs two identical machines
- CNo account is taken for change in iron losses due to flux distortion on full load conditions
- DAll of the above
20.Two dc shunt machines 200 KW each are tested by Hopkinson's test. The power input would be of the order of
- A200 kW
- B100 kW
- C35kw
- D10kW