JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II Year BASIC ELECTRICAL AND ELECTRONICS ENGINEERING Previous Question Paper (August/September - 2021 - R18)
Answer any five questions. All questions carry equal marks.
Main
Explain the KCL and KVL.
Answer
- Kirchhoff's Current Law (KCL): Also known as Kirchhoff's first law or the junction rule, it states that the algebraic sum of currents meeting at any node (or junction) in an electrical circuit is zero. Mathematically, ∑I = 0. This is a direct consequence of the Law of Conservation of Charge, implying that charge cannot accumulate at a junction.
- Kirchhoff's Voltage Law (KVL): Also known as Kirchhoff's second law or the loop rule, it states that the algebraic sum of all voltages around any closed loop in a circuit is zero. Mathematically, ∑V = 0, or the sum of potential rises equals the sum of potential drops. This is a consequence of the Law of Conservation of Energy, as the work done in moving a unit charge around a closed path must be zero.
A circuit of three resistor 15Ω, 21Ω and 39Ω respectively joined in parallel is connected in series with fourth resistance. The whole circuit is applied with 60V and is found that the power dissipated in the 15Ω resistor is 36W. Determine the value of the fourth resistance and the total power dissipated in the circuit.
Answer
- Let the parallel resistors be R1=15Ω, R2=21Ω, and R3=39Ω. Let the fourth resistor in series be R4.
- Step 1: Calculate voltage across the parallel combination (Vp). Power in R1 is P1 = Vp²/R1. Given P1=36W, 36 = Vp²/15, so Vp² = 540, Vp = √540 ≈ 23.237V.
- Step 2: Calculate total current (I). The currents in parallel branches are I1 = Vp/15, I2 = Vp/21, I3 = Vp/39. Total current I = I1 + I2 + I3 = Vp(1/15 + 1/21 + 1/39) = 23.237(0.0667 + 0.0476 + 0.0256) = 23.237(0.1399) ≈ 3.251A.
- Step 3: Calculate R4. The voltage across R4 is V4 = V_total - Vp = 60 - 23.237 = 36.763V. Since I flows through R4, R4 = V4/I = 36.763/3.251 ≈ 11.31Ω.
- Step 4: Calculate total power. Total power P_total = V_total × I = 60 × 3.251 ≈ 195.06W.
Derive the relation between line and phase quantities of voltages and currents for a star connected system?
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Define the R.M.S value and average value of an alternating quantity.
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What are the types of wires and cables? Explain.
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What are the important characteristics of batteries.
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Explain the need of power factor improvement.
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Describe the working principle of a single-phase transformer.
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A 4-pole, 300V d.c shunt generator has 720 wave connected conductors in its armature. The full load current is 50A and the flux per pole is 0.02Wb. The armature resistance is 0.3 ohms and the contact drop is 1V per brush. Calculate the full load speed of the motor.
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Derive torque equation in a D.C motor.
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A 3-phase induction motor is wound for 4 poles and is supplied from 50 Hz systems. Calculate: i) the synchronous speed ii) the speed of the motor when slip is 4% and iii) the rotor current frequency when the motor runs at 600 r.p.m.
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Explain how a p-n junction is formed and state its properties under no bias, forward bias and reverse bias condition.
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Explain the operation of center tapped full wave rectifier with neat diagram.
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With neat diagram explain the operation of p-n-p common emitter transistor.
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Compare CB, CE and CC configurations of BJT.
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