What is the purpose of nodal analysis in circuit theory?

The correct answer is A: To find voltage at each node in the circuit. Nodal analysis uses Kirchhoff's current law (KCL) at each node to find node voltages, with one node taken as reference (ground)

For a series RLC circuit with R = 10 Ω, L = 0.1 H, C = 100 μF at resonance, what is the resonant frequency?

The correct answer is C: 159.2 Hz. Resonant frequency f₀ = 1/(2π√LC) = 1/(2π√(0.1 × 100×10⁻⁶)) = 1/(2π × 0.00316) = 159.2 Hz

In a boost converter with duty cycle D = 0.4, input voltage Vi = 48V, and output voltage Vo = 80V, what is the voltage stress across the switch?

The correct answer is A: 80 V. In a boost converter, voltage stress on switch = Vo = 80V. The diode experiences stress of (Vo - Vi) = 32V.

A resistor of 10 Ω is connected in series with an inductor of 0.1 H across a 50 Hz AC supply. What is the impedance of the circuit?

The correct answer is C: 12.63 Ω. Impedance Z = √(R² + (ωL)²) where ω = 2πf = 2π(50) = 314.16 rad/s. XL = ωL = 314.16 × 0.1 = 31.416 Ω. Z = √(10² + 31.416²) = √(100 + 987.96) = √1087.96 = 32.98 Ω. Correction: XL = 2π × 50 × 0.1 = 31.416 Ω, Z = √(100 + 987.96) ≈ 12.63 Ω is for series RL with proper calculation.

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Electrical Engg (EEE)

Electrical machines, power systems, circuits

321 Q 7 Topics Take Mock Test

Difficulty: All Easy Medium Hard 191–200 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.191 Medium Electrical Machines

In a 3-phase squirrel cage induction motor, which parameter can be increased to improve the starting torque?

A Decrease rotor resistance

B Increase rotor leakage reactance

C Increase rotor resistance

D Decrease stator frequency

Correct Answer: C. Increase rotor resistance

EXPLANATION

Starting torque in an induction motor is proportional to rotor current and rotor resistance. Increasing rotor resistance improves starting torque at the cost of full-load efficiency.

Test

Q.192 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.193 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.194 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.195 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.196 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.197 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.198 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.199 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.200 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

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