JNTU
JNTU B.Tech II ELECTROMAGNETIC THEORY AND TRANSMISSION LINES Previous Question Paper (December - 2018 - 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. Each question carries 10 marks.
Part A
Point charges 1mC and -2mC are located at (3,2,-1) and (-1,-1,4) respectively. Calculate electric force on a 10nC charge located at (0,3,1).
Answer
The electric force is given by Coulomb's Law: F = (qQ / 4πε₀) * (r / |r|³). For q₁ = 1mC at P₁(3,2,-1) and q₂ = -2mC at P₂(-1,-1,4) acting on Q = 10nC at P(0,3,1), the force vectors are calculated using the displacement vectors r₁ = (-3, 1, 2) and r₂ = (1, 4, -3). Summing the individual force vectors F₁ and F₂ results in the total force on the 10nC charge.
Define electric potential and discuss its physical meaning.
Answer
Electric potential at a point is defined as the work done in moving a unit positive charge from infinity to that point against the electric field. Physically, it represents the potential energy per unit charge, indicating the capacity of the field to do work on a charge placed at that location.
State Biot-Savart’s Law.
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Define magnetic flux. What does it represent?
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Define Brewster angle.
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State poynting theorem. Does it apply to static fields explain.
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Define primary and secondary constants of a transmission line.
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What is loading? What are different types of loading?
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Define reflection coefficient and VSWR.
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A finite length loss less open circuited transmission line can act as a circuit reactive element. Justify the statement.
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Part B
Derive the expression for capacitance of a spherical capacitor.
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Conducting spherical shells with radii a=16cm and b=30cm are maintained at a potential difference of 100V such that V(r=b)=0 and V(r=a)=100V. Determine voltage and electric field in the region between the shells.
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Define linearity, homogeneity and isotropy of materials in relation to electric field.
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Electric field intensity at the surface of conductor must be perpendicular to the surface. Why is this condition necessary?
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State Ampere’s law. Discuss its application in finding magnetic field intensity due to infinite line current.
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Calculate Magnetic field intensity due to a current element of length 2 mm located at the origin in free space that carries current 16mA in the y direction.
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Given the magnetic vector potential A = ρ^2 / 4 a_z Wb/m. Calculate the total magnetic flux crossing the surface Φ=π/2, 1 < ρ < 2m, 1 < z < 5m.
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Derive Lorentz force equation.
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Explain the reflection of plane wave at oblique incidence for parallel polarization.
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An EM wave travels in space with E=100e^j(0.866y+0.5z)a_x V/m. Determine ω, λ, H and time average power.
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Explain wave propagation in lossy dielectrics and hence derive the expression for E and H fields.
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Explain power loss in plane conductor.
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A 15km line is terminated in its characteristic impedance. At a certain frequency the voltage at 1km from sending end is 9% below the sending end. Determine the voltage across load impedance in terms of percentage of sending end voltage.
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Derive the transmission line equations in terms of sending end voltages and currents.
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Derive the expression for velocity of propagation on a transmission line. What are the conditions for a lossless line?
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The characteristic impedance of a certain line is 710|14° Ω and propagation constant is 0.007+j0.028 per km. The line is terminated in 300Ω resistor. Calculate the input impedance of line if its length is 100km.
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What is the property of λ/4 line? For λ/4 line prove that ZsZr = Zo^2, Where Zs is the sending end impedance, Zr is the load impedance and Zo is the characteristic impedance. Show how this λ/4 line can be used for impedance matching.
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Find the length and position of short circuit stub to match (60+j80)Ω load to a 50Ω line at f=1GHz. Use smith chart. Explain the method.
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Characteristic impedance of a low loss transmission line is 90 Ω and it is terminated by another impedance of (130-j980)Ω. The wavelength of the line is 2.6m. Determine: i) VSWR, ii) Maximum impedance and iii) Minimum impedance.
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Give the design equations and steps for single stub matching using smith chart.
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