Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech II ELECTRICAL CIRCUITS Previous Question Paper (October - 2020 - R13)
Answer any five questions. All questions carry equal marks.
Main
Differentiate between ideal and practical voltage and current sources and write a short note on source transformation with an example.
Answer
An ideal voltage source maintains a constant terminal voltage regardless of the current drawn, having zero internal resistance. A practical voltage source includes a series internal resistance, causing the terminal voltage to drop as load current increases. An ideal current source delivers a constant current regardless of the terminal voltage, having infinite internal resistance. A practical current source includes a parallel internal resistance, causing the output current to decrease as the terminal voltage increases.
Source transformation allows a voltage source (V) in series with a resistor (R) to be replaced by a current source (I = V/R) in parallel with the same resistor R, and vice versa. This technique simplifies circuit analysis by reducing the number of nodes or loops. For example, a 10V source in series with a 2Ω resistor is equivalent to a 5A current source in parallel with a 2Ω resistor.
Perform Nodal analysis for the circuit shown in Figure 1 to determine all the branch voltages and currents.
Answer
Nodal analysis determines circuit variables using Kirchhoff's Current Law (KCL) at each non-reference node. To perform the analysis:
- Assign a reference node (ground) with 0V potential.
- Label all other independent nodes with unknown voltages (V1, V2, etc.).
- Apply KCL at each node by summing currents leaving the node to zero, expressing branch currents in terms of node voltages using Ohm's Law.
- Solve the resulting system of linear equations to find the node voltages.
- Calculate branch currents using the determined node voltages via Ohm's Law (e.g., I = (Va - Vb) / R).
Since Figure 1 is not provided, the general procedure involves setting up the nodal matrix equation
Find the source current in figure 2 if the voltage applied to the circuit is 100 volts.
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A current of 5A flows through a non-inductive resistance in series with a choking coil when supplied at 250 V, 50 Hz. If the voltage across the resistance is 125 V and across the coil is 200 V, calculate:
Impedance of the circuit, reactance and resistance of the coil.
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The power absorbed by the coil.
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The total power.
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Using fundamental concepts of sin wave derive the R.M.S Value and Average value and also find form factor and peak factor.
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A voltage of (100+j60) volts drives a current of (4-j5) Amps through a series R-L-C circuit. Determine (i) The complex expression for impedance (ii) Power consumed (iii) Power factor (iv) Draw the phasor diagram.
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A series RLC circuit has a quality factor of 5 at 50 rad/sec. The current flowing through the circuit at resonance is 10 A and the supply voltage is 100V. The total impedance of circuit is 20 Ω. Find the values of R, L and C.
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In a coupled circuit L2 = 4L1 and coupling coefficient K = 0.6. When L1 and L2 are connected in series opposing the equivalent inductance is 44.2 mH then find L1, L2 and M.
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Explain “Dot convention” used in magnetic coupled coils.
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What is duality? Explain the procedure for obtaining the dual of the given planar network shown in figure 3.
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State and explain superposition theorem.
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By using Thevenin’s theorem determine the current through 5Ω resistor shown in figure 4.
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