Q251. Servo motors are commonly used for?
A) Constant speed drives
B) Variable torque drives
C) Precise position control
D) High inertia loads
Ans: C
Explanation: Servo motors are primarily designed for accurate position and speed control in automation and robotics.
Q252. Stepper motor’s rotation is expressed in terms of?
A) Radians per second
B) Degrees per second
C) Step angle
D) Phase difference
Ans: C
Explanation: Stepper motors rotate in discrete steps, each defined by the step angle (e.g., 1.8°, 0.9°, etc.).
Q253. Which feedback device is commonly used in servo motors?
A) Potentiometer
B) Encoder
C) Resolver
D) Any of the above
Ans: D
Explanation: Depending on application precision, servo motors use potentiometers, encoders, or resolvers for position/speed feedback.
Q254. Stepper motors are commonly used in?
A) Elevators
B) CNC machines
C) Fans
D) Mixers
Ans: B
Explanation: Stepper motors are ideal for CNC machines where accurate motion control is essential.
Q255. Closed-loop control is used in which motor type?
A) DC motor
B) Stepper motor (open loop)
C) Servo motor
D) Universal motor
Ans: C
Explanation: Servo motors use closed-loop feedback to ensure precise position and speed control.
Q256. The torque produced in a stepper motor is proportional to?
A) Supply voltage
B) Step angle
C) Magnetic field strength
D) Phase current
Ans: D
Explanation: The torque depends directly on the current flowing in the stator windings.
Q257. Permanent magnet stepper motor has?
A) Variable reluctance rotor
B) Permanent magnet rotor
C) Hybrid rotor
D) None of these
Ans: B
Explanation: A PM stepper motor uses a rotor made of permanent magnets for discrete step motion.
Q258. The accuracy of a servo motor mainly depends on?
A) Load torque
B) Encoder resolution
C) Supply voltage
D) Motor speed
Ans: B
Explanation: Higher encoder resolution leads to better accuracy in position feedback and control.
Q259. A 200-step per revolution stepper motor has a step angle of?
A) 1.8°
B) 2°
C) 3°
D) 5°
Ans: A
Explanation: Step angle = 360° / 200 = 1.8° per step.
Q260. Hybrid stepper motor combines features of?
A) AC and DC motors
B) Permanent magnet and variable reluctance stepper motors
C) Servo and induction motors
D) Shunt and series motors
Ans: B
Explanation: A hybrid stepper motor uses both permanent magnet and variable reluctance principles for high torque and accuracy.
Q261. Which one requires feedback for proper functioning?
A) Stepper motor
B) Servo motor
C) Induction motor
D) Universal motor
Ans: B
Explanation: Servo motors require feedback to maintain precise control of motion.
Q262. Holding torque in stepper motors is?
A) Torque when motor is stopped
B) Torque at maximum speed
C) Zero torque condition
D) Torque during acceleration
Ans: A
Explanation: Holding torque is the torque that keeps the rotor stationary against external forces.
Q263. The main disadvantage of a stepper motor is?
A) Low cost
B) High precision
C) Loss of steps under load
D) No feedback requirement
Ans: C
Explanation: In open-loop operation, steps can be lost if the load exceeds torque capability.
Q264. A servo motor is best suited for?
A) Constant torque
B) Variable speed and position
C) High power drives
D) Continuous operation
Ans: B
Explanation: Servo systems are used where variable speed and position control are required.
Q265. Stepper motors operate using?
A) DC supply only
B) AC supply only
C) Pulsed input signals
D) Variable voltage
Ans: C
Explanation: Stepper motors operate with digital pulse inputs, each pulse moving the motor one step.
Q266. The feedback signal in a servo system is compared with?
A) Load signal
B) Reference input
C) Motor current
D) Supply voltage
Ans: B
Explanation: Feedback is compared with the reference input to produce an error signal for correction.
Q267. The rotor of a variable reluctance stepper motor is made of?
A) Laminated steel without winding
B) Copper
C) Aluminum
D) Permanent magnets
Ans: A
Explanation: The rotor of a VR stepper motor is a soft iron core with teeth, no windings.
Q268. Which motor can start, stop, and reverse instantly?
A) Stepper motor
B) DC motor
C) Induction motor
D) Synchronous motor
Ans: A
Explanation: Stepper motors can start, stop, and reverse instantly due to their discrete stepping nature.
Q269. The servo motor torque-speed characteristic is?
A) Constant torque
B) Linear
C) Non-linear
D) Drooping
Ans: C
Explanation: Torque decreases with speed — non-linear characteristic.
Q270. The open-loop control system in motion control is most likely to use?
A) DC servo motor
B) Stepper motor
C) AC servo motor
D) Induction motor
Ans: B
Explanation: Stepper motors are generally used in open-loop position control systems.
Q271. The control signal of a DC servo motor is?
A) Pulse
B) Voltage
C) Frequency
D) Current
Ans: B
Explanation: DC servo motors are controlled by input voltage, proportional to desired position/speed.
Q272. Micro-stepping in stepper motors is used to?
A) Increase speed
B) Reduce current
C) Improve resolution and smoothness
D) Reduce cost
Ans: C
Explanation: Micro-stepping divides full steps into smaller increments for smoother motion.
Q273. The feedback element in a servo system provides?
A) Amplification
B) Error correction
C) Actual output value
D) Speed increase
Ans: C
Explanation: The feedback device reports the actual position/speed to compare with the reference.
Q274. Stepper motors lose synchronization due to?
A) Low current
B) High acceleration or load
C) Proper feedback
D) Correct wiring
Ans: B
Explanation: If the load torque or acceleration exceeds the motor’s capacity, steps are lost.
Q275. The number of steps per revolution in a stepper motor depends on?
A) Supply voltage
B) Number of stator and rotor teeth
C) Current
D) Shaft diameter
Ans: B
Explanation: Steps per revolution = function of stator and rotor tooth count.
Q276. Servo amplifiers are used to?
A) Generate pulses
B) Drive the servo motor
C) Reduce speed
D) Filter noise
Ans: B
Explanation: The servo amplifier drives the motor according to control signals.
Q277. The direction of rotation of a stepper motor depends on?
A) Frequency
B) Voltage
C) Phase sequence of pulses
D) Load torque
Ans: C
Explanation: Changing the phase sequence of pulses reverses rotation.
Q278. The damping factor in a servo system affects?
A) Accuracy
B) Stability and response
C) Load torque
D) Supply voltage
Ans: B
Explanation: Proper damping ensures stability and good transient response.
Q279. A two-phase hybrid stepper motor typically requires how many drive signals?
A) 1
B) 2
C) 3
D) 4
Ans: B
Explanation: Hybrid stepper motors are generally 2-phase devices driven by two control signals.
Q280. The servo motor feedback loop compensates for?
A) Supply changes
B) Load disturbances
C) Encoder resolution
D) Step angle
Ans: B
Explanation: Feedback loop adjusts motor operation to counter load changes and maintain accuracy.
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