Which of the following represents the condition for maximum power transfer in a DC generator connected to external load?

The correct answer is A: External resistance = internal resistance. Maximum power transfer theorem: Load resistance equals source resistance for maximum power output

For a two-port network with H-parameters (hybrid parameters), H21 represents:

The correct answer is B: Current transfer ratio. H21 = I2/I1 (with V2=0) is the current transfer ratio or short-circuit current gain in a two-port network using hybrid parameters.

For a unity feedback system with G(s) = K/(s(s+3)(s+5)), what is the system type?

The correct answer is B: Type 1. The system type equals the number of poles at origin. Here, there is one pole at origin (s in denominator), making it Type 1.

What is the main purpose of tristate logic (three-state logic) in digital circuits?

The correct answer is B: Allow multiple outputs to share the same bus line without electrical conflicts. Tristate logic provides high, low, and high-impedance states, enabling multiple devices to connect to a single bus by controlling which device actively drives the line.

In a delta-wye (Δ-Y) conversion, if the delta resistances are RA, RB, RC, the wye resistance R1 (between node 1 and star point) is:

The correct answer is A: (RA×RB)/(RA+RB+RC). In Δ-Y conversion, each Y-resistor equals the product of adjacent Δ-resistors divided by the sum of all Δ-resistors.

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Electrical Engg (EEE)

Electrical machines, power systems, circuits

321 Q 7 Topics Take Mock Test

Difficulty: All Easy Medium Hard 221–230 of 321

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.221 Medium Electrical Machines

An induction motor operating at slip s = 0.04 has rotor frequency of 2 Hz. Find the supply frequency.

A 40 Hz

B 50 Hz

C 60 Hz

D 48 Hz

Correct Answer: B. 50 Hz

EXPLANATION

Rotor frequency = s × f. Therefore, 2 = 0.04 × f, giving f = 50 Hz

Test

Q.222 Medium Electrical Machines

A DC shunt motor shows increased speed. What could be the reason?

A Increased load

B Increased shunt field current

C Decreased shunt field current

D Increased armature resistance

Correct Answer: C. Decreased shunt field current

EXPLANATION

Speed = (V - IaRa)/(kΦ). Decreasing field current reduces flux Φ, increasing motor speed.

Test

Q.223 Medium Electrical Machines

A 100 kVA transformer has 1000 primary turns and 100 secondary turns. The turns ratio and voltage ratio are:

A k=0.1, voltage ratio=10:1

B k=10, voltage ratio=10:1

C k=0.1, voltage ratio=1:10

D k=100, voltage ratio=100:1

Correct Answer: A. k=0.1, voltage ratio=10:1

EXPLANATION

Turns ratio k = N2/N1 = 100/1000 = 0.1. Voltage ratio V1/V2 = N1/N2 = 10/1 or 10:1 (step-down).

Test

Q.224 Medium Electrical Machines

In a synchronous motor, the damper winding is used to:

A Reduce noise

B Provide starting torque (asynchronous torque)

C Reduce harmonics

D Improve power factor

Correct Answer: B. Provide starting torque (asynchronous torque)

EXPLANATION

Damper windings provide asynchronous starting torque to accelerate the rotor near synchronous speed before synchronous operation begins.

Test

Q.225 Medium Electrical Machines

What is the relationship between slip and rotor frequency in an induction motor?

A fr = s × fs

B fr = s × (1-s) × fs

C fr = (1-s) × fs

D fr = fs/s

Correct Answer: A. fr = s × fs

EXPLANATION

Rotor frequency fr = slip × stator frequency = s × fs, where fs = 50 Hz for 50 Hz supply.

Test

Q.226 Medium Electrical Machines

The power factor of an induction motor at full load is typically:

A 0.7-0.8 lagging

B 0.9-0.95 leading

C 0.85-0.95 lagging

D Unity (1.0)

Correct Answer: C. 0.85-0.95 lagging

EXPLANATION

Induction motors operate at lagging power factor (0.85-0.95) due to reactive magnetizing current required for flux production.

Test

Q.227 Medium Electrical Machines

A DC series motor is suitable for:

A Constant speed operation

B Applications requiring high starting torque

C Precision positioning

D Light load conditions

Correct Answer: B. Applications requiring high starting torque

EXPLANATION

DC series motors have high starting torque (proportional to load current) and are used in electric vehicles, cranes, and hoists.

Test

Q.228 Medium Electrical Machines

Which method is NOT used for starting a three-phase induction motor?

A Direct on line starting

B Star-delta starting

C Autotransformer starting

D Frequency variation starting

Correct Answer: D. Frequency variation starting

EXPLANATION

Standard starting methods are DOL, star-delta, autotransformer, and rotor resistance. Frequency variation is used for speed control, not starting.

Test

Q.229 Medium Electrical Machines

The starting current of a 3-phase induction motor is typically how many times the full-load current?

A 2-3 times

B 4-7 times

C 10-12 times

D 15-20 times

Correct Answer: B. 4-7 times

EXPLANATION

Induction motors draw 4-7 times full-load current during starting because rotor speed is zero and rotor resistance appears as reactance.

Test

Q.230 Medium Electrical Machines

The efficiency of a transformer is maximum when:

A Core loss = Copper loss

B Core loss = 2 × Copper loss

C Copper loss = 0

D Core loss = 0

Correct Answer: A. Core loss = Copper loss

EXPLANATION

Transformer efficiency is maximum when core loss (Pi) equals copper loss (Pcu), i.e., Pi = Pcu.

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