JNTU
JNTU B.Tech III ELECTROMAGNETIC THEORY AND TRANSMISSION LINES Previous Question Paper (May/June - 2019 - R16)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks.
PART - A
State Gauss law.
Answer
Gauss's law states that the total electric flux passing through any closed surface is equal to the total charge enclosed by that surface divided by the permittivity of free space. Mathematically, it is expressed as:
where D is the electric flux density, S is the closed surface, and Q_enc is the total charge enclosed within the surface.
Mention the differences between scalar and vector magnetic potentials.
Answer
The differences between scalar and vector magnetic potentials are as follows:
- Scalar Magnetic Potential (Vm): This is a scalar field defined such that the magnetic field intensity H is equal to the negative gradient of the potential, H = -∇Vm. It is only applicable in current-free regions (where J = 0) and is analogous to the electric scalar potential.
- Vector Magnetic Potential (A): This is a vector field defined such that the magnetic flux density B is equal to the curl of the potential, B = ∇ × A. It is universally applicable in all regions, including those with current sources (J ≠ 0), and is derived from the relation ∇ · B = 0.
- Scope: While the scalar potential is limited to source-free regions, the vector potential is a more general formulation that satisfies the Poisson equation ∇2A = -μJ, allowing for the calculation of magnetic fields in the presence of current distributions.
If the flux flowing through closed surface is 3 nc. What is the total charge enclosed by that surface?
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Find the input impedance of a section of a 50 Ω lossless transmission line that of length 0.1 λ long and is terminated in a short circuit.
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Define reflection coefficient and VSWR.
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Derive expression for electrostatic energy of a capacitor.
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State Maxwell's four laws in derivative form.
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Find skin depth at 1GHz for copper having conductivity 5.7×107 mho/m.
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What are the different types of loading?
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What are characteristics of infinite transmission line?
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PART - B
Derive Poisson's and Laplace's equations from fundamentals. List few of its applications concerned to electrostatic fields.
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An infinitely long uniform line charge is located at y=3, z=5. If ρl=30 nc/m, find field intensity E at (i) infinity (ii) P(3, 4, 2).
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State and prove coulomb’s law.
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Distinguish between conduction and convection currents.
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Derive the boundary conditions at the interface between (a) Dielectric-Dielectric (b) Dielectric-conductor.
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Derive Maxwell's equations in integral form. Based on this obtain the corresponding differential equation by applying Stroke's theorem.
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State and prove Biot-Savart’s law.
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Evaluate the reflection and transmission coefficients for the case of an electromagnetic wave in air incident normally upon the copper sheet at frequency of 1 MHz.
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Find the energy stored in a standing wave incident normally on a perfect conductor over a distance -λ/4 to 0 per unit in x, y coordinates.
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State and prove Poynting theorem and also write its applications.
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Derive the equation in conducting medium. Discuss skin effect and find the skin depth at 1 GHz for copper having conductivity 5.7×107 mho/m.
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Discuss in brief about inductance loading of telephone cables.
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A lossless transmission line of length 0.434 lambda and characteristic impedance 100 Ω is terminated in an impedance 260 + j 180 Ω. Find (i) Voltage reflection co-efficient (ii) Standing wave ratio (iii) Input Impedance.
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The attenuation constant on a 50 ohm distortionless transmission line is 0.01 dB/m. The line has a capacitance of 0.1 nF/m. Find the resistance, inductance and conductance per meter of the line.
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A loss less line of 100 ohms is terminated by a load which produces SWR=3. The first maximum is found to be occurring at 320cm. If f=300 MHz determine the load matching.
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Write a short notes on reflection losses on unmatched transmission line.
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The input impedance of a s short-circuited lossy transmission line of length 2m and characteristic impedance 75 Ω is 45+j225 Ω. (i) Find α and β of the line. (ii) Determine the input impedance if load is ZL=67.5 - j4.5 Ω.
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Determine the input impedance of the transmission lines of length λ/4, λ/2 and λ/8.
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A line having Zo of 100 ohms is terminated into a load of 50 - j 50 ohms. It is desired to provide matching between the line and the load by means of a short circuit stub. Determine the length of the stub if signal frequency is 10 KHz.
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