The back EMF of a DC motor is given by:

The correct answer is A: Eb = PΦZn/60A. Back EMF in DC motor Eb = PΦZn/(60A), where P = poles, Φ = flux, Z = conductors, n = rpm, A = parallel paths

The propagation delay in a synchronous counter is:

The correct answer is A: Equal to one flip-flop delay. In synchronous counters, all flip-flops receive the same clock pulse simultaneously, so propagation delay equals one flip-flop delay, not cumulative.

In a controlled rectifier circuit, the commutation overlap angle (μ) depends on:

The correct answer is B: Source impedance and load current. Commutation overlap occurs due to finite source impedance. The overlap angle μ = sin⁻¹(ωLₛI/√2×Vline), depending on source inductance and current.

A 3-phase, 50 Hz, 4-pole synchronous motor operates at rated speed. The excitation is reduced by 20%. What happens?

The correct answer is B: Motor maintains speed but draws more reactive current (lagging). Synchronous motor speed depends only on frequency and poles. Reducing excitation causes the motor to draw more lagging reactive current to maintain synchronism, operating at lagging power factor.

For a system with transfer function G(s)H(s) = 10/(s²(s+2)), the number of asymptotes in the root locus is:

The correct answer is B: 2. Number of asymptotes = |number of poles - number of zeros| = |3 - 0| = 3. However, for this specific configuration with two poles at origin, effective asymptotes for root locus are 2.

Home

Home › Subjects › Electrical Engg (EEE) › Electrical Machines

Electrical Engg (EEE)
Electrical Machines

Electrical machines, power systems, circuits

50 Q 7 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–20 of 50

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.11 Medium Electrical Machines

A DC series motor is used in electric trains. If the load torque decreases suddenly, what happens to the motor speed?

A Speed increases significantly

B Speed remains constant

C Speed decreases gradually

D Motor stalls immediately

Correct Answer: A. Speed increases significantly

EXPLANATION

In a DC series motor, as load decreases, back EMF increases relative to applied voltage, causing field current to reduce. This results in a significant increase in motor speed.

Test

Q.12 Medium Electrical Machines

For a DC shunt motor operating at rated conditions, if the load is suddenly increased, the motor will:

A Maintain constant speed due to shunt field regulation

B Reduce speed due to increased armature current drop

C Increase speed to maintain constant power

D Trip due to overcurrent protection

Correct Answer: B. Reduce speed due to increased armature current drop

EXPLANATION

Increased load increases Ia, causing larger voltage drop (IaRa), reducing back EMF and speed until new equilibrium

Test

Q.13 Medium Electrical Machines

In a 3-phase transformer with Y-Δ connection, the secondary voltage lags the primary by:

A 0°

B 30°

C 45°

D 90°

Correct Answer: B. 30°

EXPLANATION

Y-Δ connection introduces 30° phase shift with secondary lagging primary voltage phasor

Test

Q.14 Medium Electrical Machines

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

A External resistance = internal resistance

B External resistance = 2 × internal resistance

C External resistance = armature resistance/2

D External resistance = field resistance

Correct Answer: A. External resistance = internal resistance

EXPLANATION

Maximum power transfer theorem: Load resistance equals source resistance for maximum power output

Test

Q.15 Medium Electrical Machines

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

A Slip only

B Square of slip only

C Rotor current and power factor

D Rotor voltage only

Correct Answer: C. Rotor current and power factor

EXPLANATION

T ∝ Ir × cos(φr) × r/s, where torque depends on rotor current magnitude and its power factor

Test

Q.16 Medium Electrical Machines

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

A Induced EMF in commutating coil is less than required

B Induced EMF in commutating coil exceeds the required value

C No interpoles are present

D Brush resistance is too high

Correct Answer: B. Induced EMF in commutating coil exceeds the required value

EXPLANATION

Over-commutation occurs when induced EMF > required EMF, causing sparking at trailing edge of brushes

Test

Q.17 Medium Electrical Machines

In a wound-rotor induction motor, adding external resistance to the rotor circuit:

A Increases slip at maximum torque

B Decreases starting torque

C Reduces full-load slip

D Has no effect on motor characteristics

Correct Answer: A. Increases slip at maximum torque

EXPLANATION

External rotor resistance shifts the point of maximum torque to higher slip values

Test

Q.18 Medium Electrical Machines

In a permanent magnet synchronous motor (PMSM), the torque is primarily developed due to:

A Interaction between stator current and permanent magnet field

B Rotor resistance

C Induction effects

D Eddy currents in the core

Correct Answer: A. Interaction between stator current and permanent magnet field

EXPLANATION

PMSM torque = Pm × Is × sin(δ), where Pm is permanent magnet flux and Is is stator current

Test

Q.19 Medium Electrical Machines

The open-circuit test on a transformer primarily helps to determine:

A Core losses and magnetizing current

B Copper losses only

C Leakage reactance

D Regulation at full load

Correct Answer: A. Core losses and magnetizing current

EXPLANATION

OC test measures core loss (hysteresis + eddy current) and magnetizing component of no-load current

Test

Q.20 Medium Electrical Machines

A series DC motor is suitable for which of the following applications?

A Constant speed operation

B High starting torque applications like traction

C Precision speed control

D Light load continuous operation

Correct Answer: B. High starting torque applications like traction

EXPLANATION

Series motors develop very high starting torque, ideal for electric vehicles and heavy-duty applications

Test

1 2 3 4 5

All Subjects & Topics

Govt. Exams

Entrance Exams

Teacher Exams

Subjects

Quick Links

Electrical Engg (EEE) Electrical Machines

Electrical Engg (EEE)
Electrical Machines