Q1. A stepper motor is mainly used where:
A) High speed operation is required
B) Continuous rotation without control is required
C) Precise position control is required
D) High efficiency is required
Correct Option: C
Explanation: A stepper motor converts input pulses into discrete angular steps, making it ideal for precise position control in CNC machines, robotics, printers, and disk drives.
Q2. The step angle of a stepper motor depends on:
A) Supply voltage
B) Rotor inertia
C) Number of stator phases and rotor teeth
D) Load torque
Correct Option: C
Explanation: Step angle depends on number of stator phases and rotor teeth and is given by α = 360° / (m × Nr).
Q3. Which stepper motor has toothed rotor made of soft iron?
A) Permanent magnet stepper motor
B) Hybrid stepper motor
C) Variable reluctance stepper motor
D) DC servo motor
Correct Option: C
Explanation: Variable Reluctance (VR) stepper motors have soft iron toothed rotors without permanent magnets.
Q4. In a variable reluctance stepper motor, torque is produced due to:
A) Interaction of magnetic fields
B) Lorentz force
C) Rotor tendency to align with minimum reluctance path
D) Permanent magnet attraction
Correct Option: C
Explanation: Rotor always tries to align itself with minimum magnetic reluctance, producing torque.
Q5. A VR stepper motor has 4 phases and 24 rotor teeth. Find step angle.
A) 7.5°
B) 3.75°
C) 15°
D) 1.8°
Correct Option: B
Explanation: Step angle α = 360 / (4 × 24) = 3.75°.
Q6. Which stepper motor provides highest resolution (smallest step angle)?
A) VR stepper motor
B) PM stepper motor
C) Hybrid stepper motor
D) Single-stack VR motor
Correct Option: C
Explanation: Hybrid stepper motors provide very small step angles (1.8° or 0.9°) and high positional accuracy.
Q7. In a multi-stack VR stepper motor, step angle is reduced by:
A) Increasing supply frequency
B) Increasing rotor speed
C) Increasing number of stacks
D) Increasing torque
Correct Option: C
Explanation: Step angle is inversely proportional to number of stacks in a multi-stack VR motor.
Q8. A stepper motor rotates at 300 rpm with step angle 1.8°. What is pulse frequency?
A) 100 Hz
B) 300 Hz
C) 1 kHz
D) 600 Hz
Correct Option: C
Explanation: Steps/rev = 200. Pulse frequency = (300 × 200) / 60 = 1000 Hz = 1 kHz.
Q9. Which motor is inherently suitable for open-loop control?
A) Induction motor
B) DC shunt motor
C) Stepper motor
D) Synchronous motor
Correct Option: C
Explanation: Stepper motors follow input pulses accurately and do not require feedback.
Q10. In PM stepper motors, rotor is made of:
A) Laminated steel
B) Soft iron
C) Permanent magnet
D) Aluminium
Correct Option: C
Explanation: PM stepper motors use a magnetized rotor to produce higher torque.
Q11. Hybrid stepper motor combines features of:
A) PM motor + DC motor
B) VR motor + PM motor
C) DC motor + AC motor
D) Servo motor + DC motor
Correct Option: B
Explanation: Hybrid stepper motors combine toothed VR rotor and permanent magnet rotor.
Q12. The holding torque of a stepper motor is defined as:
A) Torque during acceleration
B) Torque at rated speed
C) Torque when motor is energized but stationary
D) Torque during deceleration
Correct Option: C
Explanation: Holding torque is maximum torque resisted by an energized stationary motor.
Q13. Which stepper motor has highest torque per unit volume?
A) VR stepper motor
B) PM stepper motor
C) Hybrid stepper motor
D) Multi-stack VR motor
Correct Option: C
Explanation: Hybrid stepper motors offer high torque density and compact size.
Q14. For a stepper motor, speed is directly proportional to:
A) Load torque
B) Step angle
C) Pulse frequency
D) Rotor inertia
Correct Option: C
Explanation: Speed increases with pulse frequency according to N = (f × 60) / steps per revolution.
Q15. A stepper motor has 50 rotor teeth and 4 phases. Find step angle.
A) 1.8°
B) 0.9°
C) 3.6°
D) 7.2°
Correct Option: A
Explanation: Step angle α = 360 / (4 × 50) = 1.8°.
Q16. Loss of steps in a stepper motor occurs due to:
A) Excessive load torque
B) Low inertia
C) High supply voltage
D) Proper sequencing
Correct Option: A
Explanation: When load torque exceeds motor torque, the rotor misses commanded steps.
Q17. Which stepper motor is widely used in CNC machines?
A) VR stepper motor
B) PM stepper motor
C) Hybrid stepper motor
D) Single-phase stepper motor
Correct Option: C
Explanation: CNC machines require high torque and high resolution, best provided by hybrid stepper motors.
Q18. In a multi-stack VR motor with 3 stacks, step angle is:
A) Equal to single stack
B) Double of single stack
C) One-third of single stack
D) Independent of stacks
Correct Option: C
Explanation: Step angle reduces in proportion to number of stacks.
Q19. A stepper motor completes 200 steps per revolution. Step angle is:
A) 0.9°
B) 1.8°
C) 3.6°
D) 7.5°
Correct Option: B
Explanation: Step angle = 360 / 200 = 1.8°.
Q20. A hybrid stepper motor has 200 steps/rev and is driven at 500 pps. Find speed.
A) 75 rpm
B) 150 rpm
C) 300 rpm
D) 600 rpm
Correct Option: B
Explanation: Speed N = (500 × 60) / 200 = 150 rpm.