First Year (FE)
- 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
- Using Norton's theorem, calculate the current through 3 Ω resistor across the terminals A and B in the given circuit. [Circuit: Top wire: top-left node T → 8 Ω → top-middle node P → 2 Ω → terminal A. A 3 Ω resistor is connected between A and B (right… Step 1: Norton current I_N — remove the 3 Ω and short A–B. Take node E (= B) as reference; unknowns V_P, V_D. Branch currents leaving P: thr... 1
- Find the current through 4 Ω resistance using Nodal analysis[Circuit: a common bottom wire (reference). Left branch: a 6 V battery (longer plate, +, at the top) in series with a 3 Ω resistor, going up from the bottom wire to the top-left corner; the… Assumption: the direction of the 5 A source is not marked in the figure; it is taken as delivering 5 A upward into node B (the usual form of... 1
- Explain the concept of back emf in a DC motor. When the armature of a DC motor rotates in the magnetic field, its conductors cut the flux, so an EMF is induced in them (generator action,... 1
- Explain the working principle of three phase induction motor and mention its types. Working principle of a three-phase induction motor: Rotating magnetic field: the stator carries a three-phase winding displaced by 120° in s... 1
- Explain the working principle of Brushless DC Motor. Brushless DC (BLDC) motor: a DC-supplied motor in which mechanical commutator and brushes are replaced by electronic commutation. Constructi... 1
- With the help of a neat circuit diagram explain the operation of a BJT as a switch. +Vcc | Rc LOAD (lamp/relay/LED) | +-----o Vout = V_CE | Vin o-RB--| B NPN (CE) | E | GND An NPN transistor in common-emitter configuration i... 1
- What are the losses in a single-phase transformer? A transformer has no moving parts, so there are no mechanical losses. The losses are: Iron (core) losses P_i — occur in the core due to alte... 1
- Explain the working principle of single phase transformer and derive the EMF equation. Principle: mutual induction (Faraday's law). When an alternating voltage is applied to one winding, the alternating flux it produces links t... 1
- Draw and explain the construction diagram of LED and enlist the applications. LED (Light Emitting Diode): a PN junction diode that emits light when forward biased (electroluminescence). Made of direct band-gap compound... 1
- Explain the application of Zener diode as a voltage regulator. Zener diode as a voltage regulator (shunt regulator). Rs I_L +o---/\/\/---+--------+ ^ I -> | | | I_Z | R_L V_o = V_Z Vin _|_ cathode up | |... 1
- Find RMS value of current flowing through a 314 μF capacitor when connected to 230 V, 50 Hz, single phase AC supply. Write the equation of instantaneous voltage and current. X_C = 1/2π fC = dfrac12π×50×314×10⁻⁶ = 1/0.09865 = 10.14\ Ω . RMS current: I = V/X_C = 230/10.14 = 22.69 A. V_m = 230√2 = 325.27 V; I_m = 22... 1
- A voltage e(t) = 100 sin 314 t is applied to a series circuit consisting of 10 Ω resistance, 0.0318 H inductance and a capacitor of 63.6 μF. Calculate (i) impedance of a series circuit, (ii) expression for i(t), (iii) power factor (iv) active power,… Given: V_m = 100 V, ω = 314 rad/s (f = 50 Hz), R = 10 Ω, L = 0.0318 H, C = 63.6 μF. X_L = ω L = 314×0.0318 = 9.985\ Ω ≈ 10\ Ω ; X_C = 1/ω C... 1
- Three identical coils each [4.2 + j5.6] Ω are connected in star across 415 V, three-phase, 50 Hz, AC supply. Determine (a) the line current (b) the power factor and (c) the total power. Z_ph = 4.2 + j5.6 = √(4.2² + 5.6²)∠tan⁻¹(5.6/4.2) = 7∠53.13^°\ Ω . Star: V_ph = 415/sqrt3 = 239.6 V. (a) Line current: I_L = I_ph = 239.6/7... 1
- Find supply current, current in each branch and total power factor. [Circuit (dark photograph; values partly illegible in the source scan): an AC source marked "~" at the bottom, labelled approximately "230 V, 50 Hz" (first digits unclear), feeds two… Assumed data (values read from the partly illegible figure): V = 230 V, 50 Hz; branch 1: R₁ = 10 Ω, L = 0.12 H; branch 2: R₂ = 10 Ω, C = 60... 1
- Define the following terms in the series RLC resonance circuit (i) Resonance Frequency, (ii) Resonance curve, (iii) Half-power frequencies or Cut-off frequencies, (iv) Bandwidth, (v) Quality factor (i) Resonance frequency f_r: the frequency at which X_L = X_C, so the circuit impedance is purely resistive (Z = R, minimum), current is max... 1
- State the condition of maximum power transfer in a circuit and write the expression for maximum power. Condition: a linear DC network delivers maximum power to a load resistance R_L when the load resistance is equal to the Thevenin (internal)... 1
- Find the current through 8 Ω resistance using Thevenin's Theorem. [Circuit diagram: printed as an almost completely black (over-darkened) box in the source scan; element values and connections cannot be read — partly illegible in the source scan.] Note: the circuit for this question is illegible in the source scan, so the numerical answer cannot be computed here. The complete Thevenin... 1