In an induction motor, the torque under running conditions is proportional to:

The correct answer is C: Rotor current and power factor. T ∝ Ir × cos(φr) × r/s, where torque depends on rotor current magnitude and its power factor

Which of the following represents the De Morgan's law correctly?

The correct answer is B: (A.B)' = A'+B'. De Morgan's law states: (A.B)' = A'+B' (NAND equals OR of inverted inputs) and (A+B)' = A'.B' (NOR equals AND of inverted inputs).

Which of the following is a sequential logic circuit?

The correct answer is C: Flip-flop. Flip-flops are sequential logic circuits with memory; others are combinational circuits without memory

For an underdamped second-order system, the relationship between settling time ts and damping ratio ζ is:

The correct answer is C: ts ∝ 1/(ζωn). Settling time ts ≈ 4/(ζωn) for 2% criterion, thus ts ∝ 1/(ζωn)

The commutation in a DC machine is said to be 'overcommutated' when:

The correct answer is B: Induced EMF in commutating coil exceeds the required value. Over-commutation occurs when induced EMF > required EMF, causing sparking at trailing edge of brushes

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Electrical Engg (EEE)
Electrical Machines

Electrical machines, power systems, circuits

27 Q 7 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 27

Topics in Electrical Engg (EEE)

All Circuit Analysis 100 Electrical Machines 100 Power Systems 100 Control Systems 100 Power Electronics 100 Electrical Measurements 40 Digital Electronics 100

Q.1 Easy Electrical Machines

A shaded pole induction motor uses ________ for starting torque generation.

A Capacitor

B Shaded pole or copper ring

C External resistance

D Mechanical switch

Correct Answer: B. Shaded pole or copper ring

EXPLANATION

Shaded pole motors use a copper ring or shaded pole around part of the pole face to create a phase shift in the magnetic field, producing starting torque without additional components.

Test

Q.2 Easy Electrical Machines

In a transformer, the no-load current lags the applied voltage by approximately:

A 0°

B 45°

C 90°

D 180°

Correct Answer: C. 90°

EXPLANATION

At no-load, the transformer draws mainly reactive (magnetizing) current, which lags the applied voltage by approximately 90°, giving a power factor of about 0.1-0.2.

Test

Q.3 Easy Electrical Machines

A 3-phase induction motor has 4 poles and operates from a 50 Hz supply. The synchronous speed is:

A 1500 rpm

B 3000 rpm

C 750 rpm

D 1200 rpm

Correct Answer: A. 1500 rpm

EXPLANATION

Synchronous speed Ns = 120f/P = (120 × 50)/4 = 1500 rpm for a 4-pole motor at 50 Hz.

Test

Q.4 Easy Electrical Machines

In an autotransformer, if primary turns = 100 and secondary turns = 400, the voltage transformation ratio is:

A 4:1

B 1:4

C 1:3

D 3:1

Correct Answer: B. 1:4

EXPLANATION

In an autotransformer, the turns ratio is N2/N1 = 400/100 = 4/1, so voltage transformation ratio is Vs/Vp = 1:4 for a step-up autotransformer.

Test

Q.5 Easy Electrical Machines

The rotating magnetic field in a 3-phase induction motor rotates at:

A Synchronous speed

B Slip speed

C Rotor speed

D Half of synchronous speed

Correct Answer: A. Synchronous speed

EXPLANATION

The rotating magnetic field produced by the 3-phase stator winding rotates at synchronous speed (Ns = 120f/P), independent of load or rotor speed.

Test

Q.6 Easy Electrical Machines

A transformer has primary turns = 1000, secondary turns = 100. If primary current is 2 A, what is the secondary current (neglecting losses)?

A 0.2 A

B 2 A

C 20 A

D 200 A

Correct Answer: C. 20 A

EXPLANATION

Using transformer equation: Np/Ns = Is/Ip; 1000/100 = Is/2; Is = 20 A

Test

Q.7 Easy Electrical Machines

What is the typical slip value for a squirrel-cage induction motor operating at full load?

A 0-2%

B 3-5%

C 10-15%

D 20-25%

Correct Answer: B. 3-5%

EXPLANATION

Full load slip for squirrel-cage motors typically ranges from 3-5% for good efficiency

Test

Q.8 Easy Electrical Machines

A 3-phase induction motor has 4 poles and operates at 50 Hz. What is the synchronous speed?

A 1250 rpm

B 1500 rpm

C 2400 rpm

D 3000 rpm

Correct Answer: B. 1500 rpm

EXPLANATION

Ns = 120f/P = 120×50/4 = 1500 rpm

Test

Q.9 Easy Electrical Machines

In a transformer, the hysteresis loss depends on which of the following factors?

A Frequency and maximum flux density only

B Frequency, maximum flux density, and material property

C Current and resistance only

D Voltage and impedance

Correct Answer: B. Frequency, maximum flux density, and material property

EXPLANATION

Hysteresis loss = η × B^1.6 × f × V, where η is Steinmetz constant, material property is crucial

Test

Q.10 Easy Electrical Machines

A 8-pole, 3-phase induction motor is required to run at approximately 720 RPM at 50 Hz. The approximate slip required is:

A 0.04 or 4%

B 0.08 or 8%

C 0.12 or 12%

D 0.20 or 20%

Correct Answer: A. 0.04 or 4%

EXPLANATION

Ns = 120f/P = (120 × 50)/8 = 750 RPM. For Nr = 720 RPM, s = (750 - 720)/750 = 30/750 = 0.04 or 4%.

Test

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Electrical Machines