BT-104 Basic Electrical & Electronics Engineering - Jun 2024 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aDiscuss about ideal voltage source and ideal current source with neat diagram. How ideal voltage source can be converted into ideal current source.
   How to answer

   • Define ideal voltage source: constant terminal voltage independent of load, zero internal resistance, V-I characteristic
   • Define ideal current source: constant current independent of load, infinite internal resistance, V-I characteristic
   • Neat diagrams for both with symbols
   • Source transformation: voltage source Vs in series with Rs converts to current source Is=Vs/Rs in parallel with Rs and vice-versa
2. 7 Marks
   bState and explain the superposition theorem with suitable example.
   How to answer

   • Statement of superposition theorem for linear bilateral networks
   • Steps: consider one source at a time, replace others by internal impedance, add responses
   • Illustrative example with two sources and calculation of branch current/voltage
   • Limitations/conditions
3. 7 Marks
   aUsing the mesh analysis, find the current through $5\Omega$ resistor in the network as shown in figure below.

   How to answer

   • Define meshes and assign mesh currents including 4A current source constraint
   • Form supermesh equations for meshes involving current source
   • Solve mesh equations using KVL with 100V source and resistors 20 ohm, 5 ohm, 3 ohm, 2 ohm, 1 ohm
   • Compute current through 5 ohm resistor with magnitude and direction
4. 7 Marks
   bDefine the following: i) Average value of AC voltage ii) RMS value of AC voltage iii) Power factor iv) Active power v) Reactive power vi) Apparent power vii) Three phase balanced supply
   How to answer

   • Give formula and meaning of average and RMS values for sinusoidal AC
   • Define power factor, active (kW), reactive (kVAR), apparent (kVA) power with formulas
   • Define three-phase balanced supply with equal magnitudes and 120 deg displacement
   • Mention units and phasor/power triangle where relevant
5. 7 Marks
   aDraw Phasor diagram of a 3-phase delta connected load and find the relation between phase line voltage and currents.
   How to answer

   • Draw delta triangle with phase voltages/currents and line values
   • Show phasor diagram with 120 deg displacement
   • Derive $V_L = V_{ph}$ and $I_L = \sqrt{3} I_{ph}$ with 30 deg lag
   • State assumptions of balanced load
6. 7 Marks
   bA 220 volt, 50 Hz supply is given to a series R, L, C circuit having a resistance of $50\Omega$, Inductance of 0.2H and capacitance of $100\,\mu\text{F}$. Calculate impedance, Current in the circuit and Voltage across R, L, C.
   How to answer

   • Compute inductive reactance $X_L=2\pi fL$ and capacitive reactance $X_C=1/(2\pi fC)$
   • Compute impedance $Z=\sqrt{R^2+(X_L-X_C)^2}$ and current $I=V/Z$
   • Compute voltages $V_R=IR$, $V_L=IX_L$, $V_C=IX_C$
   • Comment on inductive/capacitive nature
7. 7 Marks
   aDiscuss about magnetization characteristics of ferromagnetic material.
   How to answer

   • Define magnetization, magnetic domains, B-H curve
   • Explain initial, saturation region and hysteresis
   • Discuss permeability variation and retentivity/coercivity
   • Sketch B-H/magnetization characteristic
8. 7 Marks
   bDraw the complete phasor diagram of a single phase transformer for an inductive load. Also write the notations used for all voltages and currents used in the phasor diagram.
   How to answer

   • Draw complete phasor for transformer on inductive load with primary/secondary voltages and currents
   • Include no-load current, core loss and magnetizing components
   • Label all notations: V1, V2, I1, I2, I0, Ic, Im, E1, E2, phi
   • Explain phase lags due to inductive load
9. 7 Marks
   aWhat do you understand by self inductance and mutual inductance. Derive the relation between self inductance and mutual inductance.
   How to answer

   • Define self inductance due to own flux and mutual inductance due to coupled coil
   • Derive flux linkage relations and coefficient of coupling k
   • Derive relation $M = k\sqrt{L_1 L_2}$
   • Give units and example of coupled coils
10. 7 Marks
    bExplain the construction and working principle of a DC machine with the help of neat diagram.
    How to answer

    • List main parts: yoke, poles, armature, commutator, brushes
    • Explain construction with neat labelled diagram
    • Explain working principle: motoring/generating action, Fleming rules, commutation
    • Mention EMF/torque production
11. 7 Marks
    aDiscuss about the Torque - slip characteristics of 3-Phase Induction Motor.
    How to answer

    • Define slip and torque production in induction motor
    • Sketch torque-slip curve marking starting, maximum, full-load and synchronous points
    • Explain low-slip, high-slip and stable/unstable regions
    • Relate rotor resistance and supply voltage effects
12. 7 Marks
    bA 6 pole alternator running at 1200 rpm supplies a three phase induction motor wounded for 4 poles. If the rotor induced emf makes 3 alternator per second. Find the actual rotor speed.
    How to answer

    • Compute alternator supply frequency $f = PN/120$ from 6-pole 1200 rpm
    • Relate rotor induced emf alternations (3 per sec) to slip frequency
    • Compute slip $s = f_r/f$ and synchronous speed of 4-pole motor
    • Compute actual rotor speed $N_r = N_s(1-s)$
13. 7 Marks
    aWhat do you understand by semiconductor. Explain the different types of semiconductors in details.
    How to answer

    • Define semiconductor and energy band concept
    • Distinguish intrinsic vs extrinsic (n-type, p-type) semiconductors
    • Explain doping, charge carriers, conductivity
    • Give examples Si, Ge and applications
14. 7 Marks
    bWhat is the need of full adder circuit? Design a Full adder circuit with truth table and logic diagram.
    How to answer

    • Explain need of full adder for adding three bits including carry
    • Give truth table for sum and carry outputs
    • Derive Boolean expressions and design using gates/half-adders
    • Show logic diagram
15. 14 Marks
    Write a short note on any two : a) Star Delta Transformation b) J-K Flip-Flop c) Laws of Electromagnetic Induction d) Power in balanced and Unbalanced Three Phase System
    How to answer

    • Select any two topics from star-delta, JK flip-flop, EMI laws, balanced/unbalanced power
    • Give definition/principle, formula or truth table, diagram
    • Mention applications
    • Keep concise short-note format