1. The main objective of designing a DC machine is to:
(A) Obtain desired voltage, current, and speed with maximum efficiency and minimum cost
(B) Increase weight and size
(C) Reduce mechanical strength
(D) Ignore magnetic properties
2. The magnetic circuit of a DC machine consists of:
(A) Yoke, poles, armature core, and air gap
(B) Commutator and brushes
(C) Shaft and bearings
(D) Field winding only
3. The yoke of a DC machine serves to:
(A) Provide mechanical support and a return path for magnetic flux
(B) Hold commutator segments
(C) Reduce armature reaction
(D) Increase current flow
4. The pole core in a DC machine is made of:
(A) Laminated steel to reduce eddy current losses
(B) Solid iron
(C) Aluminum
(D) Copper
5. The field winding is placed on:
(A) The poles of the DC machine
(B) The armature core
(C) The commutator
(D) The shaft
6. The armature winding of a DC machine is:
(A) Placed in slots of the armature core
(B) Wound around poles
(C) Fixed on the shaft
(D) Mounted on the yoke
7. The commutator in a DC machine is used to:
(A) Convert AC induced in armature into DC output
(B) Increase magnetic field strength
(C) Reduce friction
(D) Cool the windings
8. The brushes in a DC machine are usually made of:
(A) Carbon or graphite
(B) Copper
(C) Aluminum
(D) Silver
9. The main losses in a DC machine include:
(A) Copper loss, iron loss, and mechanical loss
(B) Core loss only
(C) Copper loss only
(D) Friction loss only
10. The air gap in a DC machine is kept as small as possible to:
(A) Reduce magnetizing current
(B) Increase cooling
(C) Reduce armature weight
(D) Improve commutation
11. The commutation process in DC machines is improved by using:
(A) Interpoles and compensating windings
(B) Large air gap
(C) Thick commutator bars
(D) Increased speed
12. Interpoles are connected in:
(A) Series with the armature winding
(B) Parallel with the field winding
(C) Series with the shunt field
(D) Across the brushes
13. The compensating winding in a DC machine is used to:
(A) Neutralize armature reaction under load
(B) Reduce noise
(C) Improve cooling
(D) Increase field flux
14. The efficiency of a DC machine depends on:
(A) Copper, iron, and mechanical losses
(B) Speed only
(C) Voltage only
(D) Air gap length only
15. The magnetic flux per pole in a DC machine is limited by:
(A) Core saturation
(B) Brush material
(C) Commutator design
(D) Cooling arrangement
16. The specific magnetic loading in DC machine design refers to:
(A) Average flux density in the air gap
(B) Armature current density
(C) Speed of rotation
(D) Voltage per coil
17. The specific electric loading refers to:
(A) Total current per meter of armature periphery
(B) Total flux in the core
(C) Air-gap length
(D) Armature resistance
18. Increasing the specific magnetic loading generally:
(A) Reduces the size of the machine
(B) Increases the efficiency
(C) Decreases the losses
(D) Reduces armature reaction
19. Increasing the specific electric loading:
(A) Increases copper losses and temperature rise
(B) Decreases efficiency
(C) Reduces flux
(D) Improves commutation
20. The armature core is laminated to:
(A) Reduce eddy current losses
(B) Increase mechanical strength
(C) Increase hysteresis losses
(D) Improve cooling
21. The number of poles in a DC machine affects:
(A) Frequency of flux reversal and commutation
(B) Shaft diameter only
(C) Insulation thickness
(D) Field resistance
22. The commutator segments are made of:
(A) Hard-drawn copper
(B) Cast iron
(C) Brass
(D) Aluminum
23. The brush contact loss in a DC machine depends on:
(A) Brush material and current density
(B) Air gap length
(C) Pole shape
(D) Shaft speed only
24. The cooling of DC machines is improved by:
(A) Using fans and air ducts in the frame
(B) Reducing number of poles
(C) Increasing armature resistance
(D) Decreasing commutator diameter
25. The output equation of a DC machine relates:
(A) Power developed to specific magnetic and electric loadings
(B) Speed to air gap flux
(C) Voltage to frequency
(D) Torque to core length
26. The field form factor is used to represent:
(A) The ratio of RMS to average value of flux density waveform
(B) Voltage regulation
(C) Copper loss
(D) Commutation quality
27. The length-to-pole pitch ratio in DC machine design affects:
(A) Commutation and ventilation
(B) Shaft weight
(C) Field coil resistance
(D) Bearing size
28. Armature reaction in a DC machine causes:
(A) Distortion and weakening of main field flux
(B) Increase in efficiency
(C) Improvement in commutation
(D) Reduced temperature rise
29. The neutral plane of a DC machine is:
(A) The plane where no emf is induced in the armature conductors
(B) The plane of maximum flux
(C) The plane of brushes only
(D) The axis of armature current
30. The overall design of a DC machine aims to:
(A) Achieve required performance with optimum efficiency, reliability, and cost
(B) Maximize size and losses
(C) Reduce life span
(D) Ignore thermal considerations