JNTU
JNTU B.Tech II BASIC ELECTRICAL ENGINEERING Previous Question Paper (October - 2020 - R15)
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Main
What is maximum power transfer theorem? Prove the theorem.
Answer
The maximum power transfer theorem states that a resistive load connected to a DC network receives maximum power from the source when the load resistance is equal to the Thevenin equivalent resistance of the network as seen from the load terminals.
To prove this, represent the network by its Thevenin equivalent circuit consisting of a voltage source Vth in series with a resistance Rth connected to a load resistance RL. The current I flowing through the load is:
The power P delivered to the load is:
To find the condition for maximum power, differentiate P with respect to RL and set the derivative to zero:
This simplifies to:
Since the second derivative is negative at this point, RL = Rth is the condition for maximum power transfer.
Three resistances of 25 Ω, 50 Ω and 100 Ω are connected in parallel. If the total current drawn is 32 A, calculate the current drawn by each resistor.
Answer
In a parallel circuit, the voltage V across each resistor is the same. The equivalent resistance Req is given by:
The total voltage V is:
The current through each resistor is calculated using Ohm's Law (I = V/R):
- I1 = (3200/7) / 25 = 128/7 ≈ 18.29 A
- I2 = (3200/7) / 50 = 64/7 ≈ 9.14 A
- I3 = (3200/7) / 100 = 32/7 ≈ 4.57 A
Calculate the equivalent resistance across terminals P and Q for the network shown below.
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Find the average value, RMS value and the form factor of the sinusoidal waveform.
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Prove that the average value of any symmetrical wave over a complete cycle is zero.
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In an R-L-C Series circuit, the voltage across R is 160 V, across L is 240 V, and total power consumed is 1000 W, when a voltage of 200 V at 50 Hz is applied across the circuit. Calculate value of the capacitor and the current flowing through the circuit.
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Draw and explain the equivalent circuit of a transformer under the no – load condition.
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Explain the necessary tests that are conducted on transformer to find the efficiency and regulation.
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Derive the emf equation of a Transformer.
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The efficiency of 400 / 200 V, 200 KVA transformer is 98.5% at full load and at 0.8 lagging power factor. At half load, 0.8 power factor lagging the efficiency is 97.5%. Calculate the values of core loss and full load copper loss.
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Explain the constructional details of a DC Machine with a neat sketch.
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A dc machine induces an emf of 240 V at 1500 rpm. Find the developed torque for an armature current of 25 A.
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Explain the following with respect to Instruments:
Indicating
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Recording
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Integrating
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