JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II Year BASIC ELECTRICAL ENGINEERING Previous Question Paper (September - 2021 - R15)
Answer any five questions. All questions carry equal marks.
Main
State and explain Maximum Power transfer theorem.
Answer
The Maximum Power Transfer Theorem states that for a given DC network with a fixed internal resistance, the maximum power is transferred from the source to the load when the load resistance is equal to the internal resistance of the source.
Mathematically, if a source has an internal resistance Rth (Thevenin resistance), the power delivered to a load RL is given by:
To find the condition for maximum power, we differentiate PL with respect to RL and set it to zero:
Solving this derivative yields the condition RL = Rth. At this point, the load receives the maximum possible power from the circuit. The efficiency of power transfer at this condition is exactly 50%, as half the power generated is dissipated as heat within the internal resistance of the source.
Find the current in the resistors R1 = 10Ω and R2 = 20Ω connected in parallel across a voltage source. The supply current is 50 A. Also, find power across each resistance.
Answer
Given two resistors in parallel, R1 = 10Ω and R2 = 20Ω, with a total supply current I = 50 A, we use the current divider rule to find the individual currents.
The current through R1 is:
The current through R2 is:
The voltage across the parallel combination is V = I1 × R1 = 33.33 × 10 = 333.3 V. The power across each resistance is calculated using P = I2R:
Using Super position theorem, find the current through the 20Ω resistor for the network shown below:
Answer
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Explain the terms with respect to Alternating Quantity: i) Instantaneous value and ii) Time period.
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If the form factor of a current waveform is 2 and the amplitude factor is 2.5, find the average value of the current if the maximum value of the current is 500 A.
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Explain the terms with respect to Alternating Quantity: i) average value ii) Root mean square value iii) Maximum value.
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A 230 V, 50 Hz voltage is applied to a coil L = 5 H and R = 2Ω is in series with a capacitance C. What value must C have in order that the voltage across the coil is 400 V?
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Derive the expression of emf induced in a transformer.
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Explain the working of transformer on lagging power factor load with a neat phasor diagram.
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Explain the various constructional features to be considered for a single phase transformer.
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In a 25 KVA, 2000/200 V transformer the iron and full load copper losses are 350 W and 400 W respectively. Find the efficiency at 0.8 power factor lagging at i) Full load and ii) Half load.
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Derive the emf equation of a dc generator.
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Explain the working of a 3-phase Induction Motor.
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Explain the working of Attraction type moving iron instrument with a neat sketch.
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