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.
A sinusoidal voltage v(t) = 300sin(100πt) V is applied to a 50 Ω resistor. What is the average power dissipated?
Answer: B
Vm = 300 V, VRMS = 300/√2 = 212.13 V, P = VRMS²/R = (212.13)²/50 = 900 W
Q.22Medium
What is the relationship between source voltage (Vs), terminal voltage (Vt), and current (I) in a real voltage source with internal resistance r?
Answer: A
In a real voltage source, terminal voltage Vt = Vs - Ir, hence Vs = Vt + Ir (accounting for voltage drop across internal resistance)
Q.23Medium
A network has two meshes with currents I₁ = 3A and I₂ = 2A. The mutual inductance between the coils is 0.5H. What is the mutual inductance voltage in the first coil due to current change in the second coil at dI₂/dt = 4 A/s?
Answer: C
Mutual inductance voltage V = M × dI/dt = 0.5 × 4 = 2V
Q.24Medium
A parallel RC circuit is connected to a 100V AC source at 50Hz. If R = 20Ω and C = 100μF, what is the total impedance of the circuit?
Answer: A
For parallel RC: Xc = 1/(2πfC) = 1/(2π×50×100×10⁻⁶) = 31.83Ω. Z = (R×Xc)/√(R²+Xc²) = (20×31.83)/√(400+1013) ≈ 15.8Ω
Q.25Medium
In mesh current analysis for a two-mesh circuit with self-resistances R₁ = 10Ω, R₂ = 15Ω and mutual resistance Rm = 5Ω, and voltages V₁ = 20V, V₂ = 0V, what would be the mesh impedance matrix determinant?
In delta-to-star transformation, if delta resistances are Ra = 30Ω, Rb = 40Ω, Rc = 50Ω, what is the star resistance R₁ (connected to point corresponding to Ra)?
What is the reactive power in an AC circuit with apparent power S = 1000VA and power factor = 0.8?
Answer: B
P = S × PF = 1000 × 0.8 = 800W. Q = √(S² - P²) = √(1000000 - 640000) = √360000 = 600 VAR
Q.29Medium
A network has 8 branches and 5 nodes. The number of independent mesh equations required is:
Answer: B
Number of independent mesh equations = b - n + 1, where b=branches, n=nodes. Here: 8 - 5 + 1 = 4
Q.30Medium
For maximum power transfer to a load from a source with Thevenin equivalent (Vth, Rth), the load resistance should be:
Answer: C
Maximum power transfer theorem: Load resistance RL should equal Thevenin resistance Rth for maximum power delivery. Maximum power = Vth²/(4Rth)
Q.31Medium
In a planar circuit, the relationship between number of nodes (n), branches (b), and independent loops (m) is:
Answer: B
For a connected planar circuit: Number of independent loops = b - n + 1 (also known as cyclomatic complexity or mesh rank)
Q.32Medium
The reciprocity theorem states that in a linear bilateral network:
Answer: C
Reciprocity theorem: If a voltage source at port 1 produces current at port 2, then the same source at port 2 produces equal current at port 1. Applicable for bilateral linear networks.
Q.33Medium
In a circuit, the star-delta transformation is used to:
Answer: D
Star-delta transformation converts between two three-terminal network configurations, simplifying circuit analysis by eliminating nodes that cannot be solved directly.
Q.34Medium
In mesh analysis, if a circuit has dependent sources, the approach is:
Answer: B
Mesh analysis works with dependent sources by expressing the controlling variable in terms of mesh currents, then solving the resulting equations.
Q.35Medium
The Norton equivalent of a network is found by:
Answer: C
Norton equivalent: IN = Isc (short-circuit current) and RN = Rth (equivalent resistance). Norton and Thevenin equivalents are related: Vth = IN × RN
Q.36Medium
In a circuit with mutual inductance between two coils, the coupling coefficient k is defined as:
Answer: B
Coupling coefficient k = M/√(L₁L₂), where 0 ≤ k ≤ 1. k=1 indicates perfect coupling, k=0 means no coupling.
Q.37Medium
In a magnetically coupled circuit with two inductors L₁ and L₂ with mutual inductance M, if current increases in primary, the induced voltage in secondary opposes this change. This demonstrates:
Answer: C
Faraday's law describes EMF generation; Lenz's law describes the direction (opposition to change). Both apply to mutual inductance phenomena.
Q.38Medium
A network is said to be bilateral if:
Answer: B
Bilateral networks are linear networks where reciprocal relationships hold. Networks with ideal diodes are unilateral (non-bilateral).
Q.39Medium
For a two-port network, if Z-parameters are known, the relationship between input impedance and Z11 is:
Answer: C
Z11 is defined as input impedance with port 2 open-circuited (I2=0). Therefore, Zin = Z11 only under this condition.
Q.40Medium
In a circuit with a dependent voltage source controlled by current, the controlling current flows through:
Answer: C
A CCVS (Current-Controlled Voltage Source) depends on current through any element in the control branch, measured in the specified reference direction.
