A second-order system has damping ratio ζ = 0.5. What is the nature of its response?

The correct answer is B: Underdamped with oscillations. For ζ < 1, the system is underdamped and exhibits oscillatory response. At ζ = 0.5, there are definitely oscillations with exponential decay.

What happens to the impedance of a series RLC circuit when frequency approaches resonant frequency?

The correct answer is B: Impedance decreases and becomes minimum (equal to R). At resonance, XL = XC, so Z = √(R² + (XL - XC)²) = R (minimum). This occurs at f₀ = 1/(2π√LC)

In phase plane analysis, what does a limit cycle represent?

The correct answer is B: A stable oscillation with constant amplitude. A limit cycle is a closed trajectory in phase plane representing self-sustained oscillations with constant amplitude and frequency, independent of initial conditions.

What is the Norton equivalent current (In) for a circuit where the short-circuit current between terminals A and B is 5A?

The correct answer is B: 5A. Norton equivalent current is equal to the short-circuit current measured between the terminals, which is 5A.

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

The correct answer is C: 35.7 kVAR. 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).

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Electrical Engg (EEE)

Electrical machines, power systems, circuits

321 Q 7 Topics Take Mock Test

Difficulty: All Easy Medium Hard 51–60 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.51 Medium Electrical Measurements

What is the main limitation of analog instruments in automated data acquisition systems?

A Lower measurement accuracy

B Inability to provide direct digital output for computer interfacing

C Higher temperature stability

D Better frequency response

Correct Answer: B. Inability to provide direct digital output for computer interfacing

EXPLANATION

Analog instruments cannot directly interface with digital computers; they require ADC conversion for data acquisition systems.

Test

Q.52 Medium Electrical Measurements

In a potentiometer method for EMF comparison, if standard cell EMF is 1.018 V with 106.4 cm length, and unknown cell requires 107.8 cm, what is unknown EMF?

A 1.026 V

B 1.031 V

C 1.018 V

D 1.035 V

Correct Answer: B. 1.031 V

EXPLANATION

E₂/E₁ = L₂/L₁; E₂ = (107.8/106.4) × 1.018 ≈ 1.031 V.

Test

Q.53 Medium Electrical Measurements

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

A Maximum positive voltage

B Minimum (approximately zero)

C Maximum negative voltage

D Voltage equals excitation voltage

Correct Answer: B. Minimum (approximately zero)

EXPLANATION

At null position in LVDT, the core is centered, and secondary voltages from both coils cancel out, resulting in zero or minimum output.

Test

Q.54 Medium Electrical Measurements

A standard cell has an EMF of 1.0186 V at 20°C with temperature coefficient of -0.0004 V/°C. What will be its EMF at 25°C?

A 1.0186 V

B 1.0170 V

C 1.0180 V

D 1.0202 V

Correct Answer: B. 1.0170 V

EXPLANATION

EMF at 25°C = 1.0186 - 0.0004 × (25-20) = 1.0186 - 0.002 = 1.0166 ≈ 1.0170 V.

Test

Q.55 Medium Electrical Measurements

In a megohmmeter, what voltage is typically applied across the test terminals to measure very high resistances (> 1 MΩ)?

A 1 kV to 5 kV DC

B 230 V AC only

C 100 V DC

D 50 V AC

Correct Answer: A. 1 kV to 5 kV DC

EXPLANATION

Megohmmeters use high DC voltages (1-5 kV) to force sufficient current through high resistances for measurable deflection.

Test

Q.56 Medium Electrical Measurements

An AC bridge circuit is used to measure unknown capacitance. At balance, the product of opposite arms satisfies which condition?

A Z₁ × Z₃ = Z₂ × Z₄

B Z₁/Z₂ = Z₃/Z₄

C Z₁ × Z₄ = Z₂ × Z₃

D Z₁ + Z₃ = Z₂ + Z₄

Correct Answer: C. Z₁ × Z₄ = Z₂ × Z₃

EXPLANATION

For AC bridges at balance condition: Z₁ × Z₄ = Z₂ × Z₃, where Z represents impedance of arms.

Test

Q.57 Medium Electrical Measurements

Which method is most suitable for measuring frequency in the range of 10 Hz to 100 kHz with high accuracy in 2024-25 standards?

A Lissajous pattern method using CRO

B Digital frequency counter with microprocessor

C Resonance method with LC circuit

D Stroboscopic method

Correct Answer: B. Digital frequency counter with microprocessor

EXPLANATION

Digital frequency counters provide accuracy of ±1 count with real-time display and are industry standard for this frequency range.

Test

Q.58 Medium Electrical Measurements

A wattmeter with voltage coil rating of 300 V and current coil rating of 5 A is used to measure power in a circuit. If the actual voltage is 250 V and current is 4 A at power factor 0.8, what will be the wattmeter reading if it has full-scale deflection of 1500 W?

A 800 W

B 960 W

C 1200 W

D 1000 W

Correct Answer: A. 800 W

EXPLANATION

Power = V × I × cos(φ) = 250 × 4 × 0.8 = 800 W. The wattmeter reading equals actual power consumed.

Test

Q.59 Medium Electrical Measurements

A moving coil galvanometer has an internal resistance of 10 Ω and a full-scale deflection current of 5 mA. What shunt resistance is required to convert it into an ammeter with a range of 0-5 A?

A 0.01 Ω

B 0.02 Ω

C 0.05 Ω

D 0.1 Ω

Correct Answer: A. 0.01 Ω

EXPLANATION

Shunt resistance Rs = (Ig × Rg)/(I - Ig) = (5×10^-3 × 10)/(5 - 5×10^-3) ≈ 0.01 Ω

Test

Q.60 Medium Electrical Measurements

The null deflection method in bridge circuits is preferred over deflection method because it:

A Is faster

B Eliminates errors due to calibration and non-linearity of meter

C Requires less power

D Uses less expensive components

Correct Answer: B. Eliminates errors due to calibration and non-linearity of meter

EXPLANATION

Null deflection (or balance) method is preferred because it doesn't depend on meter calibration or linearity. The measurement relies on the balance condition formula only.

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