Which of the following is the SI unit of electric current?
Answer: A
Ampere (A) is the SI base unit of electric current. It is defined as the flow of one coulomb of charge per second.
Q.2Medium
A moving coil galvanometer has a coil resistance of 10 Ω and gives full-scale deflection for 5 mA current. What shunt resistance is required to convert it into an ammeter of range 0-5 A?
Answer: A
Using shunt formula: S = (Ig × Rg) / (I - Ig) = (5×10⁻³ × 10) / (5 - 5×10⁻³) ≈ 0.01 Ω
Q.3Easy
The accuracy of an electrical measuring instrument is expressed as a percentage of:
Answer: C
In electrical measurements, accuracy is typically expressed as a percentage of full scale deflection (FSD) or full scale reading (FSR) for analog instruments.
Q.4Hard
A voltmeter has an internal resistance of 100 kΩ and shows a reading of 50 V across a 1 MΩ resistor. What is the true voltage across the resistor?
Answer: C
The voltmeter and resistor form a parallel circuit. Using voltage divider: V_true = 50 × (1000 + 100) / 1000 ≈ 54.55 V
Q.5Medium
Which bridge circuit is most suitable for measuring an unknown capacitance?
Answer: C
Owen bridge is specifically designed for accurate measurement of unknown inductance and capacitance values in AC circuits.
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Q.6Easy
The error in an ammeter connected in series with a circuit is primarily due to:
Answer: B
An ideal ammeter should have zero internal resistance. Non-zero internal resistance causes voltage drop and measurement error.
Q.7Medium
In a Wheat stone bridge, the null deflection is obtained when the ratio of resistances satisfies which condition?
Answer: B
At balance condition in Wheatstone bridge: R₁/R₂ = R₃/R₄, which can be rearranged to R₁ × R₄ = R₂ × R₃
Q.8Medium
A moving iron instrument reads the same for both AC and DC because it:
Answer: A
Moving iron instruments deflect based on the magnitude of current/voltage regardless of direction. The iron core is attracted by the magnetic field produced by the coil in both AC and DC.
Q.9Easy
The class of accuracy for a class 1.5 instrument means:
Answer: C
The accuracy class (e.g., 1.5, 2.0) indicates the maximum percentage error with respect to full scale deflection, as per IEC standards.
Q.10Medium
A thermocouple is used to measure temperature because it:
Answer: D
Thermocouples generate EMF (Seebeck effect) proportional to the temperature difference between junctions and don't require external power.
Q.11Hard
For accurate power measurement in a three-phase system with unbalanced load, the minimum number of wattmeters required is:
Answer: C
For unbalanced three-phase loads, three wattmeters are required—one in each phase—to measure total power accurately.
Q.12Medium
The mutual inductance between two coils is independent of:
Answer: C
Mutual inductance depends on geometry, coil configuration, and medium properties, but NOT on the current flowing through them.
Q.13Medium
A platinum resistance thermometer (RTD) follows which relationship between resistance and temperature?
Answer: B
RTDs exhibit a nearly linear relationship between resistance and temperature: Rt = R₀(1 + αt + βt²), where the linear term dominates.
Q.14Easy
The input impedance of a digital multimeter is typically:
Answer: C
Modern digital multimeters have very high input impedance (typically 10 MΩ for voltage measurement) to minimize loading effects on the circuit.
Q.15Easy
In a CRO (Cathode Ray Oscilloscope), the Y-deflection sensitivity is expressed in:
Answer: A
Y-deflection sensitivity (or gain) in CRO is expressed in volts per division, indicating how many volts are represented by each vertical division.
Q.16Medium
A Hall effect sensor is primarily used to measure:
Answer: B
Hall effect sensors detect the magnetic field strength by measuring the Hall voltage generated when a current-carrying conductor is placed in a perpendicular magnetic field.
Q.17Medium
The power factor of a circuit can be improved by adding:
Answer: C
Power factor (lagging) is improved by adding shunt capacitance, which creates a leading current that offsets the lagging component.
Q.18Easy
The sensitivity of a galvanometer is defined as:
Answer: A
Sensitivity of a galvanometer is the deflection (in mm or degrees) produced per unit current (usually per microampere or milliampere).
Q.19Hard
In an AC bridge at balance condition, if R₁ = 100 Ω, R₂ = 50 Ω, and R₃ (inductive) = 200 Ω with series R, then R₄ is:
Answer: A
Using AC bridge balance: Z₁/Z₂ = Z₃/Z₄; therefore 50100 = 200/Z₄, which gives Z₄ = 100 Ω
Q.20Medium
The null deflection method in bridge circuits is preferred over deflection method because it:
Answer: B
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.
