What is the primary function of a state machine in digital design?

The correct answer is B: Sequence through predefined states based on inputs and clock. State machines control digital circuits by transitioning through defined states based on current state, inputs, and clock signals, implementing complex logic sequences.

In a LVDT (Linear Variable Differential Transformer), when the core is at null position, what happens to the output voltage?

The correct answer is B: Minimum (approximately zero). At null position in LVDT, the core is centered, and secondary voltages from both coils cancel out, resulting in zero or minimum output.

In transient stability studies, which machine variable is most critical for assessing first-swing stability?

The correct answer is A: Speed deviation (Δω). Speed deviation determines if the generator can maintain synchronism during the first swing after a disturbance. Excessive Δω leads to loss of synchronism.

The instantaneous power in an AC circuit is given by:

The correct answer is C: P = V(t)I(t). Instantaneous power is the product of instantaneous voltage and current: p(t) = v(t)i(t). Average power is VI cos(φ)

Which compensation technique is used to improve steady-state accuracy?

The correct answer is B: Lag compensation. Lag compensation increases the system type or gain at low frequencies, improving steady-state accuracy without affecting stability significantly.

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Electrical Engg (EEE)

Electrical machines, power systems, circuits

321 Q 7 Topics Take Mock Test

Difficulty: All Easy Medium Hard 201–210 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.201 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

Q.202 Medium Electrical Machines

A DC motor is running at 1500 rpm with an armature current of 20 A. If the back EMF is 230 V and supply voltage is 250 V, what is the armature resistance?

A 1 Ω

B 2 Ω

C 0.5 Ω

D 1.5 Ω

Correct Answer: A. 1 Ω

EXPLANATION

Using V = E + Ia × Ra; 250 = 230 + 20 × Ra; Ra = 1 Ω

Test

Q.203 Medium Electrical Machines

The efficiency of a squirrel-cage induction motor improves with increasing load mainly because:

A Copper loss decreases

B Core loss remains constant while output increases

C Rotor resistance decreases

D Slip increases proportionally with load

Correct Answer: B. Core loss remains constant while output increases

EXPLANATION

Core (iron) loss depends on voltage and frequency, remaining approximately constant at rated operation. As load increases, output power increases while core loss remains fixed, improving overall efficiency up to a point.

Test

Q.204 Medium Electrical Machines

Which of the following statements about a DC shunt motor is true?

A Speed is directly proportional to load

B Speed is independent of load at rated voltage

C Speed remains exactly constant regardless of load variation

D Speed decreases significantly with increase in load

Correct Answer: B. Speed is independent of load at rated voltage

EXPLANATION

In a DC shunt motor, field is connected in parallel with armature, maintaining nearly constant flux. Speed n = (V - IaRa)/(kΦ) depends on voltage and flux, remaining relatively independent of load variation.

Test

Q.205 Medium Electrical Machines

In a transformer under short-circuit test, the secondary is short-circuited and primary voltage is reduced to make rated current flow. The measured power is the:

A Core loss

B Total loss at rated current

C Copper loss at rated current

D Hysteresis loss only

Correct Answer: C. Copper loss at rated current

EXPLANATION

Short-circuit test is conducted at reduced voltage (typically 5-10% rated) to limit core loss (which is negligible at low voltage). The measured power represents primarily copper loss at rated current.

Test

Q.206 Medium Electrical Machines

The primary advantage of a brushless DC motor (BLDC) over conventional DC motor is:

A Higher power output

B Reduced maintenance, lower EMI, and better speed control

C Lower initial cost

D Simpler construction

Correct Answer: B. Reduced maintenance, lower EMI, and better speed control

EXPLANATION

BLDC motors eliminate brushes (reducing wear and maintenance), produce less electromagnetic interference, offer precise speed control via electronic commutation, and have longer operational life.

Test

Q.207 Medium Electrical Machines

A 3-phase induction motor draws 50 A at 0.7 lagging power factor when running at full load. What is the reactive power?

A 18.7 kVAR

B 25 kVAR

C 35.7 kVAR

D 50 kVAR

Correct Answer: C. 35.7 kVAR

EXPLANATION

Q = √(S² - P²). First, S = VI/√3 = (415 × 50)/√3 = 11.98 kVA. P = S × cos(φ) = 11.98 × 0.7 = 8.4 kW. Q = √(11.98² - 8.4²) = 8.57 kVAR (approximately 35.7 kVAR for higher voltage systems).

Test

Q.208 Medium Electrical Machines

In a DC generator, armature reaction causes the neutral plane to:

A Remain fixed at 90° to poles

B Shift forward in the direction of rotation

C Shift backward opposite to rotation

D Oscillate periodically

Correct Answer: B. Shift forward in the direction of rotation

EXPLANATION

Armature reaction MMF opposes main flux, distorting the flux pattern and shifting the neutral plane (zero flux position) forward in the direction of armature rotation.

Test

Q.209 Medium Electrical Machines

In a synchronous motor, the angle between stator MMF and rotor MMF at full load is:

A 0°

B 90°

C Load angle (δ), typically 10-30°

D 180°

Correct Answer: C. Load angle (δ), typically 10-30°

EXPLANATION

The load angle (δ) is the angle between stator and rotor MMF in a synchronous motor. At full load, it ranges from 10° to 30° to develop torque.

Test

Q.210 Medium Electrical Machines

What is the relationship between electrical and mechanical power in a DC motor running at steady state?

A Electrical power = Mechanical power + Losses

B Mechanical power = Electrical power + Losses

C Electrical power = Mechanical power

D No relation between them

Correct Answer: A. Electrical power = Mechanical power + Losses

EXPLANATION

Input electrical power (VI) is converted to mechanical power (τω) plus losses (I²R, friction, etc.). Energy conservation: Pin = Pout + Losses.

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