JNTU
JNTU B.Tech II NETWORK THEORY Previous Question Paper (October - 2020 - R16)
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Main
Find the flux produced in the magnetic core in the circuit shown in figure 1? Given Area of cross section of the core is 4 cm2 and the relative permeability of the core is 1500.
Answer
To find the magnetic flux in the core, we use the analogy between magnetic and electric circuits. The magnetic flux φ is given by the ratio of the magnetomotive force (MMF) to the reluctance (S) of the core.
1. Calculate the Reluctance (S): The reluctance is defined as S = l / (μ0 μr A). Assuming a mean path length l (typically provided in the circuit diagram, let's denote it as l in meters), the area A = 4 cm2 = 4 × 10-4 m2, and relative permeability μr = 1500. Given μ0 = 4π × 10-7 H/m, the reluctance is:
2. Calculate the MMF: The MMF is the product of the number of turns N and the current I flowing through the coil (MMF = NI). Obtain these values from the provided circuit diagram.
3. Calculate the Flux (φ): Using the magnetic Ohm's law:
Substituting the calculated values into the formula yields the total flux in Webers (Wb). Ensure all units are in SI (meters, Amperes, Henrys) before final calculation.
What is dot convention? Explain with an example.
Answer
The dot convention is a standard method used to indicate the relative polarity of the voltages induced in mutually coupled coils. When current enters the dotted terminal of one coil, the induced voltage at the dotted terminal of the other coil is positive with respect to its undotted terminal.
For example, in two mutually coupled coils with self-inductances L1 and L2 and mutual inductance M, if a time-varying current i1 enters the dot of coil 1, a voltage v2 = M(di1/dt) is induced at the dotted terminal of coil 2. This convention simplifies the analysis of coupled circuits by allowing the sign of the mutual inductance term to be determined by inspection.
Draw the graph for the following circuit and find ‘V’ using tieset matrix.
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Explain the relationship between phase and line quantities in three phase star connected systems.
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Two wattmeters are connected to measure the input power to a balanced 3-phase load by the two wattmeter method. If the instruments readings are 6kW and 4kW, the total power and load power factor are respectively.
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Discuss in detail about the measurement of reactive power in three phase circuits.
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Three identical coils each of resistance 20Ω and inductance 50.3mH are connected in delta to a 440V, 50Hz, 3-phase supply. Calculate the rms value of the phase current, line current and the power factor.
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Discuss in detail about the transient response of series RLC circuit with step input.
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Explain in detail about the transient response of series RC circuit with a) impulse input b) step input.
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Discuss in detail about Z-parameters.
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For the two port network shown in figure 2, find hybrid parameters.
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With the help of neat sketch, explain in detail about the design of high pass filter.
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