For a control system, the gain crossover frequency and phase crossover frequency are equal. What does this indicate about the system's stability margin?

The correct answer is C: System is marginally stable. When gain crossover frequency equals phase crossover frequency, the system is at the stability boundary (phase = -180°), indicating marginal stability.

Which of the following Boolean expressions is equivalent to (A+B)·(A+C)?

The correct answer is A: A + BC. Using distribution law: (A+B)·(A+C) = A + BC (Consensus theorem verification)

A proportional controller with Kp = 10 is applied to a unity feedback system with G(s) = 1/[s(s+2)]. The velocity error constant Kv is:

The correct answer is A: 5. Kv = lim[s→0] s·Kp·G(s) = lim[s→0] s·10·1/[s(s+2)] = 10/2 = 5

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

In a three-phase balanced system, if the line voltage is 400V, what is the phase voltage?

The correct answer is A: 230.9 V. In a balanced three-phase system, VL = √3 × Vph. Therefore, Vph = VL/√3 = 400/√3 = 400/1.732 = 230.9 V

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Electrical Engg (EEE)

Electrical machines, power systems, circuits

196 Q 7 Topics Take Mock Test

Difficulty: All Easy Medium Hard 111–120 of 196

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.111 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.112 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.113 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.114 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.115 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.116 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.117 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.118 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.119 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

Q.120 Easy Electrical Machines

The no-load core loss in a transformer is primarily due to:

A Copper losses in windings

B Hysteresis and eddy current losses in core

C Friction in mechanical parts

D Leakage flux

Correct Answer: B. Hysteresis and eddy current losses in core

EXPLANATION

No-load losses consist of hysteresis loss (due to core magnetization reversal) and eddy current loss (due to induced currents in core material). Copper loss occurs only under load.

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