JNTU
JNTU B.Tech II ELECTROMAGNETIC THEORY AND TRANSMISSION LINES Previous Question Paper (May - 2019 - R15)
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.
Part A
What is polarization? Give an expression that accounts for polarization in an isotropic material.
Answer
Polarization is the process of displacement of bound charges in a dielectric material under the influence of an external electric field, resulting in the creation of electric dipoles. For an isotropic material, the polarization vector P is related to the electric field E by the expression:
where ε₀ is the permittivity of free space and χₑ is the electric susceptibility of the material.
State the continuity equation. What is its significance?
Answer
The continuity equation is given by:
Its significance is that it represents the principle of conservation of charge, stating that the net current flowing out of a closed surface must equal the rate of decrease of charge within the volume enclosed by that surface.
State the Maxwell’s Equations for good conductors.
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What is Lorentz Force Law? How does it relate mechanical force to electrical force?
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What is the expression of attenuation constant and phase constant for wave propagation in good conductors?
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Define Brewster angle and Critical angle.
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What are the two types of copper losses?
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What are the characteristics of a low loss line?
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What is Current Standing wave Ratio (CSWR)?
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For what purpose is a quarter wave length transmission line used? Explain.
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Part B
Obtain the expression for electric field due to Line charge density.
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A point charge of 5nC lies at (0,1,0) and an infinite line charge at 10 nC/m along z-axis. Find E at (2, 3, 1).
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Derive the expression of Gauss’s Law for a uniformly charged sphere.
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Three point charges Q1=30nC, Q2=40nC and Q3=-70nC are enclosed by surface S. What is the net flux that crosses S?
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State Amphere’s Circuit Law. Find H at (-3, 4, 0) due to a current element along x-axis.
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Find an expression for the magnetic field produced by a straight current carrying conductor at a distance “x” from it.
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Give an example of displacement current. Also state few differences between conduction current density and displacement current density.
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Given E=10 Sin (ωt-βz)ay V/m in free space, determine D, B and H.
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Discuss wave propagation in lossless media and in free space.
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The electric field intensity associated with a plane wave travelling in a perfect dielectric medium is given by Ex (z, t) = 10 Cos(2π×10^7 t -0.1πz)V/m. Find the magnetic field intensity associated with the wave if μ=μ0.
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Derive the expression for total time average power through a surface.
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A uniform plane wave is incident normally on an infinitely thick slab of a material with 25V/m electric field. The material has a dielectric constant 4. How much power penetrates the material slab?
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Derive the expression for the input impedance of a uniform transmission line.
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What is loading? What are the types of loading?
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An 8 km transmission line is terminated by a characteristic impedance z0. The voltage at 1 km from the sending end is 10% below that at the sending end. What is the voltage across the load impedance in terms of % of the sending end voltage?
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Discuss the advantages and disadvantages of stub matching.
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An arial of (200-j300)Ω is to be matched with 500Ω lines. The matching is to be done by means of a low loss line 600Ω stub line. Find the position and length of the stub line used if the operating wavelength is 20 m.
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What is a Smith chart? Explain its significance.
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Write a brief note on the various impedance matching techniques.
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