The main reason for power loss in rotor is

 Q1. The speed of an induction motor is always:

A) Equal to synchronous speed
B) Greater than synchronous speed
C) Less than synchronous speed
D) Zero
Answer: C
Explanation: Due to slip, the rotor speed is always slightly less than the synchronous speed in an induction motor.

---

Q2. The rotating magnetic field in a 4-pole, 50 Hz induction motor rotates at:
A) 750 rpm
B) 1000 rpm
C) 1500 rpm
D) 3000 rpm
Answer: C
Explanation: Ns = 120f/P = 120×50/4 = 1500 rpm.

---

Q3. The slip of an induction motor at synchronous speed is:
A) Zero
B) One
C) Infinity
D) Negative
Answer: B
Explanation: Slip $S = \frac{N_s - N}{N_s}$; when $N = 0$, $S = 1$.

---

Q4. The frequency of rotor current at standstill is:
A) Zero
B) Same as supply frequency
C) Twice the supply frequency
D) Half the supply frequency
Answer: B
Explanation: At standstill, rotor speed is zero; so frequency $f_r = s f = f$.

---

Q5. The torque of an induction motor is maximum when:
A) Slip = 1
B) Rotor reactance = Rotor resistance
C) Slip = 0
D) Supply voltage = 0
Answer: B
Explanation: Condition for maximum torque: $R_2 = s X_2$.

---

Q6. The starting torque of a squirrel cage induction motor is:
A) Very high
B) Low
C) Zero
D) Infinite
Answer: B
Explanation: Due to low rotor resistance, starting torque is low.

---

Q7. The type of rotor used in a slip ring induction motor is:
A) Squirrel cage
B) Wound rotor
C) Permanent magnet
D) DC commutator type
Answer: B
Explanation: Slip ring induction motors use a wound rotor with external resistances.

---

Q8. The slip of an induction motor under normal running condition is about:
A) 0.001
B) 0.05
C) 0.2
D) 1.0
Answer: B
Explanation: Slip is typically 2–5% at full load.

---

Q9. Crawling occurs in induction motors due to:
A) Harmonics
B) Poor cooling
C) Excessive slip
D) Low voltage
Answer: A
Explanation: 7th harmonic torque causes crawling at about 1/7th synchronous speed.

---

Q10. Double cage induction motor is used to obtain:
A) High starting torque
B) High efficiency
C) Constant speed
D) Low cost
Answer: A
Explanation: The outer cage has high resistance, giving high starting torque.

---

Q11. In an induction motor, rotor copper losses are proportional to:
A) Slip
B) 1/Slip
C) Slip²
D) Speed
Answer: A
Explanation: Rotor Cu loss = s × rotor input power.

---

Q12. In an induction motor, the air-gap power is equal to:
A) Stator input
B) Rotor output
C) Stator copper loss
D) Rotor input power
Answer: D
Explanation: Air-gap power is the power transferred from stator to rotor.

---

Q13. The main disadvantage of a squirrel cage motor is:
A) High cost
B) Low efficiency
C) Low starting torque
D) Maintenance problems
Answer: C
Explanation: Low rotor resistance causes low starting torque.

---

Q14. The torque-speed curve of an induction motor is:
A) Linear
B) Parabolic
C) Hyperbolic
D) Drooping characteristic
Answer: D
Explanation: It rises sharply and then decreases with speed.

---

Q15. Slip is defined as:
A) Ratio of rotor speed to synchronous speed
B) Difference between synchronous and rotor speed divided by synchronous speed
C) Ratio of torque to current
D) Ratio of frequency to voltage
Answer: B
Explanation: $s = \frac{N_s - N}{N_s}$.

---

Q16. If slip = 0.04 and Ns = 1500 rpm, rotor speed N = ?
A) 1440 rpm
B) 1500 rpm
C) 1560 rpm
D) 1350 rpm
Answer: A
Explanation: $N = N_s(1 - s) = 1500(1 - 0.04) = 1440 \text{ rpm}$.

---

Q17. The efficiency of an induction motor is maximum when:
A) Slip is large
B) Slip is small
C) Torque is high
D) Supply voltage is high
Answer: B
Explanation: Smaller slip reduces rotor copper losses → higher efficiency.

---

Q18. The power factor of an induction motor is:
A) Leading at all loads
B) Lagging at all loads
C) Unity
D) Leading at no load
Answer: B
Explanation: The magnetizing current makes power factor lagging.

---

Q19. The direction of rotation of an induction motor can be reversed by:
A) Changing rotor connections
B) Reversing supply voltage
C) Interchanging any two supply leads
D) Changing rotor resistance
Answer: C
Explanation: Interchanging two phases reverses rotating magnetic field direction.

---

Q20. In no-load condition, an induction motor draws:
A) Very small current
B) Large magnetizing current
C) Zero current
D) Purely resistive current
Answer: B
Explanation: No-load current mainly consists of magnetizing current.

---

Q21. The torque developed by an induction motor is proportional to:
A) Slip
B) 1/slip
C) s/(R² + s²X²)
D) Frequency
Answer: C
Explanation: $T \propto \frac{sE_2^2R_2}{R_2^2 + (sX_2)^2}$.

---

Q22. The starting current of a squirrel cage induction motor is:
A) 2 times full-load current
B) 3–5 times full-load current
C) 6–8 times full-load current
D) 10–12 times full-load current
Answer: C
Explanation: High inrush current due to low rotor impedance at standstill.

---

Q23. The slip of an induction motor at no load is approximately:
A) 0.1
B) 0.01
C) 0.001
D) 1
Answer: C
Explanation: At no load, speed is almost synchronous → very small slip.

---

Q24. Induction motor is called a:
A) Constant speed motor
B) Variable speed motor
C) DC motor
D) Commutator motor
Answer: A
Explanation: Speed variation with load is very small, hence constant speed.

---

Q25. The torque of an induction motor depends on:
A) Voltage squared
B) Voltage
C) Current
D) Frequency
Answer: A
Explanation: $T \propto V^2$.

---

Q26. The main reason for power loss in rotor is:
A) Hysteresis
B) Eddy currents
C) Copper losses
D) Friction
Answer: C
Explanation: Power lost as I²R losses in rotor winding.

---

Q27. The speed of an induction motor decreases with:
A) Increase in load
B) Decrease in load
C) Decrease in voltage
D) Increase in frequency
Answer: A
Explanation: More load → more torque required → more slip → less speed.

---

Q28. In 3-phase induction motor, the torque is produced due to:
A) Magnetic attraction
B) Magnetic repulsion
C) Induction interaction
D) Lenz’s law
Answer: D
Explanation: Lenz’s law opposes the cause of flux variation → torque production.

---

Q29. Which component produces rotating magnetic field?
A) Rotor
B) Stator
C) Shaft
D) Frame
Answer: B
Explanation: Three-phase currents in stator windings create a rotating magnetic field.

---

Q30. Slip rings are used in:
A) Squirrel cage motor
B) Wound rotor motor
C) DC motor
D) Stepper motor
Answer: B
Explanation: To connect external resistance to rotor.

---

Q31. For maximum torque, the slip is:
A) Directly proportional to rotor resistance
B) Inversely proportional to rotor resistance
C) Independent of resistance
D) Equal to rotor reactance
Answer: A
Explanation: $s_{max} = R_2 / X_2$.

---

Q32. The speed control of induction motor can be done by:
A) Varying supply frequency
B) Adding resistance in stator
C) Changing rotor slots
D) Adjusting pole pitch
Answer: A
Explanation: Frequency control directly changes synchronous speed.

---

Q33. In induction motor, blocked rotor test is used to find:
A) Magnetizing current
B) Leakage reactance and rotor resistance
C) Core loss
D) Efficiency
Answer: B
Explanation: Blocked rotor test simulates short-circuit condition.

---

Q34. No-load test determines:
A) Friction and windage losses
B) Rotor losses
C) Leakage reactance
D) Resistance
Answer: A
Explanation: With no load, mechanical losses can be measured.

---

Q35. The speed-torque characteristic of an induction motor resembles:
A) DC series motor
B) DC shunt motor
C) DC compound motor
D) Stepper motor
Answer: B
Explanation: Nearly constant speed like DC shunt motor.

---

Q36. Induction motor operates on:
A) Self-excitation
B) Electromagnetic induction
C) Commutation
D) Chemical reaction
Answer: B
Explanation: EMF induced in rotor by stator’s rotating magnetic field.

---

Q37. Rotor current frequency decreases when:
A) Slip increases
B) Speed increases
C) Load increases
D) Rotor resistance increases
Answer: B
Explanation: $f_r = s f$; as speed rises, slip decreases → lower $f_r$.

---

Q38. The mechanical power developed by the rotor = ?
A) (1 − s) × rotor input
B) s × rotor input
C) Rotor Cu loss
D) Stator Cu loss
Answer: A
Explanation: Rotor mechanical power = air-gap power × (1 − s).

---

Q39. Rotor bars are usually made of:
A) Copper or aluminum
B) Brass
C) Steel
D) Silver
Answer: A
Explanation: Conductive and economical materials for rotor bars.

---

Q40. The efficiency of an induction motor is generally:
A) 40–50%
B) 60–70%
C) 80–90%
D) 95–98%
Answer: C
Explanation: Efficiency ranges from 80% to 90% in standard motors.

---

Q41. The magnetizing component of no-load current is:
A) In phase with voltage
B) Lagging by 90°
C) Leading by 90°
D) Opposite phase
Answer: B
Explanation: Magnetizing current lags the supply voltage by 90°.

---

Q42. Slip of an induction motor can be negative when:
A) Motor runs above synchronous speed
B) Motor runs below synchronous speed
C) Motor is at standstill
D) Motor is off
Answer: A
Explanation: In generator operation (regenerative braking), slip is negative.

---

Q43. If supply frequency is increased, synchronous speed will:
A) Decrease
B) Increase
C) Remain constant
D) Be zero
Answer: B
Explanation: $N_s = 120f/P$, so speed ∝ frequency.

---

Q44. Rotor copper losses at full load are equal to:
A) s × rotor input
B) (1 − s) × rotor input
C) Total losses
D) Constant losses
Answer: A
Explanation: Copper loss = s × air-gap power.

---

Q45. The main function of the fan at the rear of the motor is to:
A) Improve torque
B) Cool the motor
C) Reduce noise
D) Increase speed
Answer: B
Explanation: Fans dissipate heat to prevent overheating.

---

Q46. Induction motor cannot run at synchronous speed because:
A) No torque is produced
B) Slip becomes 1
C) Magnetic field stops rotating
D) Supply voltage reduces
Answer: A
Explanation: At synchronous speed, no relative motion → no induced EMF → no torque.

---

Q47. If load is removed, slip becomes:
A) Zero
B) One
C) Very small
D) Very high
Answer: C
Explanation: With no load, speed ≈ synchronous → small slip.

---

Q48. Rotor induced emf per phase at standstill is:
A) s × E₂
B) E₂
C) (1 − s) × E₂
D) Zero
Answer: B
Explanation: At standstill, slip = 1, so induced emf = E₂.

---

Q49. The stator losses of an induction motor are:
A) Copper and iron losses
B) Copper only
C) Iron only
D) Mechanical losses
Answer: A
Explanation: Stator has both I²R and core losses.

---

Q50. The speed regulation of induction motor is:
A) Poor
B) Good
C) Very good
D) Zero
Answer: B
Explanation: Speed change from no load to full load is small, i.e., good regulation.