Electrical Measurements & Power Factor
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๐ Comprehensive Syllabus & Examination Guide
Electrical Measurements & Power Factor
Official curriculum roadmap, subject/topic distribution, negative marking rules, pacing guidelines, and solved sample questions.
๐ฏ Mapped Subjects & Topic Question Distribution
Total Question Pool
100%
26 MCQs
Combined Active Syllabus
Electrical Measurements & Power Factor
26 MCQs
Topic Pool
๐ Question Pool Structure
26 MCQs across fundamental, intermediate, and advanced concept tiers.
โก Recommended Pacing
45 to 60 seconds per MCQ. Flag complex problems and preserve 10 minutes for final revision.
โ๏ธ Scoring & Negative Marking
+1 mark per correct answer. In competitive tests with negative marking, -0.25 applies for incorrect guesses.
๐ก Strategic Preparation & Exam Hall Guidelines
To maximize your score on Electrical Measurements & Power Factor, candidates are advised to follow a structured three-pass approach. In the First Pass, solve all direct recall and formula-based questions within 30 seconds each to secure foundational marks. In the Second Pass, tackle multi-step analytical and quantitative reasoning problems. In the Third Pass, review marked questions and verify calculations.
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๐ Pre-Rendered Solved Sample Questions & Detailed Solutions
Review the solved problems below to understand question phrasing, answer choices, and step-by-step solution logic prior to starting the full interactive practice drill:
Sample Question 1
Electrical Measurements & Power Factor
Easy • Electrical Engineering
Permanent Magnet Moving Coil (PMMC) instruments can be used to measure:
A
Direct current (DC) quantities only
B
Alternating current (AC) quantities only
C
Both AC and DC quantities equally
D
Radio frequency currents
โ Correct Answer: A - Direct current (DC) quantities only
๐ Step-by-Step Solution & Conceptual Rationale:
PMMC instruments operate on Lorentz force (Td = B*I*N*A). With AC current, the deflecting torque reverses direction every half-cycle, resulting in zero average torque (pointer merely vibrates around zero). Therefore, PMMC inherently measures only DC (average value).
Sample Question 2
Electrical Measurements & Power Factor
Easy • Electrical Engineering
Why is the scale of a PMMC measuring instrument perfectly linear and uniform?
A
Deflecting torque is directly proportional to current (Td โ I) and controlling torque is proportional to deflection (Tc โ theta)
B
Deflecting torque is proportional to current squared
C
Eddy current damping linearizes the needle movement
D
Permanent magnets have non-linear field distribution
โ Correct Answer: A - Deflecting torque is directly proportional to current (Td โ I) and controlling torque is proportional to deflection (Tc โ theta)
๐ Step-by-Step Solution & Conceptual Rationale:
In a PMMC instrument with cylindrical soft-iron core and curved pole shoes, magnetic flux density B is uniform and radial. Deflecting torque Td = B*N*A * I. Since spring control torque Tc = C * theta, at balance Td = Tc -> theta โ I, resulting in a strictly linear, evenly-spaced scale.
Sample Question 3
Electrical Measurements & Power Factor
Easy • Electrical Engineering
Moving Iron (MI) instruments (attraction or repulsion type) can measure:
A
DC quantities only
B
Both AC and DC quantities, reading the true RMS value of AC signals
C
Peak value of AC signals only
D
Average value of AC signals
โ Correct Answer: B - Both AC and DC quantities, reading the true RMS value of AC signals
๐ Step-by-Step Solution & Conceptual Rationale:
In moving iron instruments, deflecting torque is proportional to the square of current (Td โ I^2 * dL/dtheta). Because I^2 is always positive regardless of current direction, deflecting torque is unidirectional for both AC and DC, indicating true RMS value.
Sample Question 4
Electrical Measurements & Power Factor
Easy • Electrical Engineering
Why is the scale of a Moving Iron instrument non-linear (cramped at the lower end and spread out at the upper end)?
A
Deflecting torque is proportional to the square of the operating current (Td โ I^2)
B
The damping chamber creates back pressure
C
Control springs age over time
D
The coil has high resistance
โ Correct Answer: A - Deflecting torque is proportional to the square of the operating current (Td โ I^2)
๐ Step-by-Step Solution & Conceptual Rationale:
Because deflecting torque varies with current squared (Td โ I^2), deflection theta โ I^2. Thus, the scale follows a square-law distribution, cramped closely at low current values and open at higher current values.
Sample Question 5
Electrical Measurements & Power Factor
Easy • Electrical Engineering
To convert a basic PMMC galvanometer with internal resistance Rm into an ammeter capable of measuring higher currents, one must connect:
A
A very low resistance (shunt resistor Rsh) in parallel with the meter movement
B
A high multiplier resistor in series with the meter movement
C
A capacitor in series
D
An inductor in parallel
โ Correct Answer: A - A very low resistance (shunt resistor Rsh) in parallel with the meter movement
๐ Step-by-Step Solution & Conceptual Rationale:
To extend current range, a low-resistance shunt Rsh is connected in parallel with the meter: Rsh = Rm / (m - 1), where multiplying factor m = I / Im. The majority of load current bypasses the delicate meter movement through the low-resistance shunt.
Sample Question 6
Electrical Measurements & Power Factor
Easy • Electrical Engineering
To extend the voltage measurement range of a basic PMMC meter movement to form a voltmeter, one must connect:
A
A high multiplier resistor (Rs) in series with the meter
B
A low resistance in parallel
C
A center-tapped transformer
D
A shunt capacitor
โ Correct Answer: A - A high multiplier resistor (Rs) in series with the meter
๐ Step-by-Step Solution & Conceptual Rationale:
To extend voltage range, a high resistance multiplier Rs is connected in series: Rs = Rm * (m - 1), where m = V / Vm. The series resistor drops the bulk of the applied voltage, limiting current through the coil to its safe full-scale deflection value Im.
Sample Question 7
Electrical Measurements & Power Factor
Medium • Electrical Engineering
What material is standard for manufacturing ammeter shunts and voltmeter multiplier resistors due to its near-zero temperature coefficient of resistance?
A
Pure Copper
B
Manganin (Copper-Manganese-Nickel alloy) or Constantan
C
Aluminum
D
Silicon steel
โ Correct Answer: B - Manganin (Copper-Manganese-Nickel alloy) or Constantan
๐ Step-by-Step Solution & Conceptual Rationale:
Manganin has a negligible temperature coefficient of resistance (approx. 0.00001 / deg C) and low thermal EMF against copper. This ensures that instrument calibration does not drift with ambient or I^2*R self-heating temperature changes.
Sample Question 8
Electrical Measurements & Power Factor
Medium • Electrical Engineering
Which AC bridge is specifically used for the precision measurement of an unknown capacitance and its dielectric dissipation factor (tan delta)?
A
Schering Bridge
B
Maxwell's Inductance-Capacitance Bridge
C
Anderson's Bridge
D
Wheatstone Bridge
โ Correct Answer: A - Schering Bridge
๐ Step-by-Step Solution & Conceptual Rationale:
The Schering Bridge is the industry-standard bridge for measuring capacitance and dielectric loss angle (dissipation factor tan delta = omega * C1 * r1) of high-voltage cables, transformer bushings, and insulating materials.
Sample Question 9
Electrical Measurements & Power Factor
Medium • Electrical Engineering
Maxwell's Inductance-Capacitance Bridge is most suitable for measuring the inductance of coils having:
A
Medium Quality Factor (1 < Q < 10)
B
Very high Quality Factor (Q > 10)
C
Very low Quality Factor (Q < 1)
D
Zero resistance
โ Correct Answer: A - Medium Quality Factor (1 < Q < 10)
๐ Step-by-Step Solution & Conceptual Rationale:
Maxwell's L-C bridge balances an unknown inductance against a standard variable capacitor. It is ideal for medium-Q coils (1 to 10). For high-Q coils (Q > 10), Hay's Bridge is used; for low-Q coils (Q < 1), Anderson's Bridge is preferred.
Sample Question 10
Electrical Measurements & Power Factor
Medium • Electrical Engineering
Hay's Bridge is preferred over Maxwell's Bridge for measuring inductances with:
A
High Quality Factor (Q > 10)
B
Low Quality Factor (Q < 1)
C
Zero self-capacitance
D
High mutual coupling
โ Correct Answer: A - High Quality Factor (Q > 10)
๐ Step-by-Step Solution & Conceptual Rationale:
In Hay's bridge, the resistance and capacitance in the standard arm are connected in series rather than parallel. The balance equation contains term (1 / [1 + (1/Q)^2]), which simplifies cleanly for high-Q coils (Q > 10) where (1/Q)^2 is negligible.
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