1. What is the primary advantage of using a series DC motor?
a) High efficiency
b) Simple construction
c) Smooth operation
d) Constant speed under varying loads
Answer: d) Constant speed under varying loads
2. In a series DC motor, the field winding is connected in __________ with the armature winding.
a) Series
b) Parallel
c) Series-parallel
d) None of the above
Answer: a) Series
3. Which of the following statements is true for a series DC motor under no-load conditions?
a) The speed is maximum
b) The speed is minimum
c) The speed is zero
d) The speed is constant
Answer: c) The speed is zero
4. What happens to the speed of a series DC motor as the load torque increases?
a) Speed increases
b) Speed decreases
c) Speed remains constant
d) Speed becomes zero
Answer: b) Speed decreases
5. The starting torque of a series DC motor is ___________ compared to other types of DC motors.
a) Higher
b) Lower
c) Same
d) Unpredictable
Answer: a) Higher
6. The speed-torque characteristic of a series DC motor is ___________.
a) Hyperbolic
b) Linear
c) Parabolic
d) Exponential
Answer: a) Hyperbolic
7. Which component is commonly used in a series DC motor to control its speed?
a) Diode
b) Capacitor
c) Rheostat
d) Transformer
Answer: c) Rheostat
8. What happens if the field winding of a series DC motor is disconnected while it’s running?
a) The motor stops immediately
b) The motor runs at full speed
c) The motor reverses direction
d) The motor continues to run at the same speed
Answer: b) The motor runs at full speed
9. A series DC motor is not suitable for applications that require ___________.
a) High starting torque
b) Variable speed control
c) Low current consumption
d) Long operational life
Answer: b) Variable speed control
10. What is the typical application of a series DC motor?
a) Ceiling fan
b) Computer hard drive
c) Electric vehicle
d) Solar power generation
Answer: a) Ceiling fan
11. What protects a series DC motor from excessive current in case of a sudden load reduction?
a) Capacitor
b) Rheostat
c) Centrifugal switch
d) Circuit breaker
Answer: c) Centrifugal switch
12. Which of the following statements is true for a series DC motor operating below its rated voltage?
a) The speed decreases
b) The speed increases
c) The speed remains constant
d) The motor stalls
Answer: a) The speed decreases
13. The torque-speed characteristic of a series DC motor shows a __________ relationship.
a) Linear
b) Hyperbolic
c) Parabolic
d) Inverse
Answer: d) Inverse
14. Which component is responsible for the commutation process in a series DC motor?
a) Armature
b) Brushes
c) Commutator
d) Field coil
Answer: c) Commutator
15. A series DC motor is not recommended for applications that require ___________.
a) High starting torque
b) Rapid acceleration
c) Minimal maintenance
d) Smooth and precise control
Answer: d) Smooth and precise control
16. What is the speed regulation of a series DC motor with increasing load?
a) Positive
b) Negative
c) Zero
d) Unpredictable
Answer: b) Negative
17. In a series DC motor, the armature current is equal to ___________.
a) Supply voltage divided by armature resistance
b) Supply voltage multiplied by armature resistance
c) Supply voltage minus armature resistance
d) Supply voltage plus armature resistance
Answer: d) Supply voltage plus armature resistance
18. The efficiency of a series DC motor is highest at ___________.
a) No-load
b) Full load
c) Half-load
d) Overload
Answer: b) Full load
19. Which type of DC motor exhibits the most considerable speed variation from no-load to full-load?
a) Series
b) Shunt
c) Compound
d) Separately excited
Answer: a) Series
20. What protects a series DC motor from armature winding damage due to excessive current?
a) Thermal overload relay
b) Voltage regulator
c) Fuse
d) Flywheel
Answer: a) Thermal overload relay
21. The back EMF (electromotive force) in a series DC motor is directly proportional to ___________.
a) Armature current
b) Armature resistance
c) Field current
d) Supply voltage
Answer: a) Armature current
22. The armature windings in a series DC motor are usually made of ___________.
a) Copper
b) Aluminum
c) Iron
d) Silver
Answer: a) Copper
23. What type of load is most suitable for a series DC motor?
a) Constant torque
b) Constant speed
c) Variable torque
d) No-load
Answer: c) Variable torque
24. In a series DC motor, reversing the direction of current through the armature will ___________.
a) Increase speed
b) Decrease speed
c) Reverse the direction of rotation
d) Have no effect on speed or rotation
Answer: c) Reverse the direction of rotation
25. What is the most common cause of armature failure in a series DC motor?
a) Overheating
b) Excessive vibration
c) Short circuit
d) Open circuit
Answer: c) Short circuit
26. The torque produced by a series DC motor is proportional to ___________.
a) Speed
b) Voltage
c) Current
d) Resistance
Answer: c) Current
27. What happens if the field winding in a series DC motor becomes open (breaks)?
a) The motor will not start
b) The motor will run at maximum speed
c) The motor will stop running
d) The motor will draw excessive current
Answer: c) The motor will stop running
28. The direction of rotation of a series DC motor can be reversed by ___________.
a) Changing the field winding polarity
b) Changing the armature winding polarity
c) Changing the direction of armature current
d) Changing the direction of field current
Answer: c) Changing the direction of armature current
29. In a series DC motor, the speed can be controlled by varying ___________.
a) Armature voltage
b) Field voltage
c) Armature current
d) Field current
Answer: c) Armature current
30. What happens to the torque produced by a series DC motor as the load
torque increases?
a) Torque increases
b) Torque decreases
c) Torque remains constant
d) Torque becomes zero
Answer: b) Torque decreases