Electrical Engineering questions for GATE, PSU recruitment and SSC JE draw from network theory, electrical machines, power systems, control systems, measurements and instrumentation, analog and digital electronics, and electromagnetic fields. Numerical answers include the formula used and the unit at each stage, which is where marks are commonly lost even when the approach is correct.
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.
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.
