Basic Electrical & Electronics Engineering
- How are three-phase voltages generated and why are they displaced by 120 degrees? In one line Three identical coils placed 120° apart on the same rotor (or stator) of an alternator produce three equal sinusoidal EMFs that... 1
- What is parallel resonance, and how does it differ from series resonance? In one line Parallel resonance occurs in a coil-capacitor parallel (tank) circuit when the reactive currents of the two branches cancel, mak... 1
- What are line and phase voltage and current relations in a balanced star connection? In one line In a balanced star (Y) connection, line voltage is √(3) times phase voltage and leads it by 30°, while line current equals phase... 1
- What are line and phase voltage and current relations in a balanced delta connection? In one line In a balanced delta (Δ) connection, line voltage equals phase voltage, while line current is sqrt3 times phase current and lags... 1
- How does source transformation convert a voltage source into an equivalent current source? In one line A practical voltage source V with series resistance R can be replaced by a current source I = V/R with the same R in parallel, a... 1
- What are Kirchhoff's current law and voltage law, and how do you apply them to a circuit? In one line Kirchhoff's Current Law (KCL) says the total current entering a node equals the total current leaving it, and Kirchhoff's Voltag... 1
- How do star-delta and delta-star transformations simplify resistor networks? In one line Star-delta transformation replaces three resistors connected in a star (Y) with an equivalent set of three in a delta (triangle)... 1
- What is the difference between ideal and practical voltage and current sources? In one line An ideal source gives a fixed voltage (or current) no matter what load is connected, while a practical source has internal resis... 1
- What does the superposition theorem state and how is it used with multiple sources? In one line In a linear circuit with several independent sources, the current or voltage in any element equals the algebraic sum of the valu... 1
- How do you solve a DC circuit using mesh analysis with mesh currents? In one line Mesh analysis assigns a loop current to each window (mesh) of a planar circuit, writes KVL for every mesh, and solves the result... 1
- How does Thevenin's theorem replace a complex network by a single source and resistance? In one line Thevenin's theorem says any linear two-terminal network can be replaced by one voltage source V_th in series with one resistance... 1
- How do you solve a DC circuit using nodal analysis with node voltages? In one line Nodal analysis picks one node as reference (0 V), writes KCL at every other node in terms of unknown node voltages, and solves f... 1
- How does Norton's theorem represent a network as a current source with parallel resistance? In one line Norton's theorem says any linear two-terminal network can be replaced by a current source I_N in parallel with a resistance R_N... 1
- What is the maximum power transfer theorem and what load resistance gives maximum power? In one line A source delivers maximum power to a load when the load resistance equals the Thevenin resistance of the source network, R_L = R... 1
- What is the working principle of a single-phase transformer and why does it not work on DC? In one line A transformer works on mutual induction: an alternating current in the primary winding sets up an alternating flux in the iron c... 1
- What are core-type and shell-type transformers and how do their constructions differ? In one line Core-type and shell-type transformers differ in how the windings and iron core are arranged: in core type the windings surround... 1
- A coil having a resistance of 10 Ω and an inductance of 40 mH is connected to a 200 V, 50 Hz supply. Calculate the impedance of the coil, current, power factor and power consumed. X_L = 2π fL = 2π×50×0.04 = 12.566\ Ω . Impedance: Z = √(10² + 12.566²) = √(257.91) = 16.06 Ω (= 10 + j12.566 = 16.06∠51.49° Ω). Current: I =... 1
- Using source transformation find the current flowing the 8 Ω resistance [Circuit: a common bottom wire. Left: an 18 V battery (longer plate, +, at the top) from the bottom wire up to the top-left corner. Top wire: top-left corner → resistor (label pr… Reading of the figure: the first series resistor is taken as 6 Ω (its label is over-struck in the print; this is the standard version of the... 1
- Differentiate between BJT and FET. PointBJTFET (JFET/MOSFET) CarriersBipolar: both electrons and holesUnipolar: only majority carriers ControlCurrent-controlled device (I_C =... 1
- Write down the relation between line current and phase current, line voltage and phase voltage, power in balanced three phase delta connected balanced load. For a balanced delta (Δ) connected load: Voltage: each phase is connected directly between two lines, so V_L = V_ph. Current: each line curr... 1
- An inductive coil having inductance of 0.04 H and resistance 25 Ω has been connected in series with another inductive coil of inductance 0.2 H and resistance 15 Ω. The whole circuit is powered with 230 V, 50 Hz mains. Calculate the power dissipation… Coil 1: R₁ = 25 Ω, X₁ = 2π(50)(0.04) = 12.566\ Ω . Coil 2: R₂ = 15 Ω, X₂ = 2π(50)(0.2) = 62.832\ Ω . Total: R = 25 + 15 = 40 Ω, X = 12.566 +... 1
- What is the necessary condition for resonance in a series circuit? Derive an expression for resonance frequency. Condition: an R-L-C series circuit is at resonance when the inductive reactance equals the capacitive reactance, X_L = X_C. Then the net rea... 1
- A balanced 3-φ, star connected load consist of three coils each consisting of R = 6 Ω and XL = 8 Ω. Determine the 1) Phase impedance 2) Phase voltage 3) Phase current 4) Line current 5) Power factor when connected across 400 V, 50 Hz supply. Given: star connection, R = 6 Ω, X_L = 8 Ω, V_L = 400 V, 50 Hz. 1) Phase impedance: Z_ph = √(6²+8²) = 10 Ω (= 6 + j8 = 10∠53.13° Ω). 2) Phas... 1
- Convert the star circuit into its equivalent delta circuit. [Figure: star network with centre N; arm N–A = 2 Ω (A at the top), arm N–B = 4 Ω (B at lower left), arm N–C = 6 Ω (C at lower right).] R_A = 2 Ω, R_B = 4 Ω, R_C = 6 Ω. Sum of products: R_AR_B + R_BR_C + R_CR_A = 2(4) + 4(6) + 6(2) = 8 + 24 + 12 = 44\ Ω² . Star → delta: R_AB... 1