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Posted Date: 25 Oct 2008 Posted By: prashanth beerelli Member Level: Diamond
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2008 Jawaharlal Nehru Technological University Electrical and Electronics Engineering II B.Tech Supplimentary Examinations, Aug/Sep 2008,ELECTROMAGNETIC WAVES AND TRANSMISSION LINES Question paper
Code No: R05220404 Set No. 1
II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008
ELECTROMAGNETIC WAVES AND TRANSMISSION LINES
( Common to Electronics & Communication Engineering and Electronics &
Telematics)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. (a) Define conductivity of a material.
(b) Apply Gauss’s law to derive the boundary conditions at a conductor-dielectric
interface.
(c) In a cylindrical conductor of radius 2mm, the current density varies with
distance from the axis according to J = 103e-400rA/m2. Find the total current
I. [4+6+6]
2. (a) State Ampere’s circuital law. Specify the conditions to be met for determining
magnetic field strength, H, based on Ampere’s circuital law
(b) A long straight conductor with radius ‘a’ has a magnetic field strength H =
(Ir/2pa2) ˆa within the conductor (r < a) and H = (I/2pr) ˆa outside the
conductor (r > a) Find the current density J in both the regions (r < and r
> a)
(c) Define Magnetic flux density and vector magnetic potential. [4+8+4]
3. (a) Derive the equation of continuity for time varying fields.
(b) A Parallel plate capacitor with a plate area of 5cm2 and plate separation
of 3mm has a voltage 50 Sin 103t V applied to its plates. Calculate the
displacement current assuming 2= 2 20 [8+8]
4. A 3 GHz uniform plane wave propagates through rexolite in the positive Z-direction
the E-field at Z = 0 is 100 6 00v/m
(a) Calculate the RMS value and phase of E at Z=4 cm
(b) Calculate the total attenuation in dB over a distance of 6 wave langths.
For rexolite 2r=2.54 and tan d=0.0005 [8+8]
5. (a) Define Complex Poynting vector and explain how to obtain an average power.
(b) A plane wave of frequency 2MHz is incident upon a copper conductor normally.
The wave has an electric field amplitude of E= 2mV/m. The copper has
er = 1, µr = 1 and s = 5.8 × 107 mho/m. Find out average power density
absorbed by the copper. [8+8]
6. (a) Explain about attenuation in parallel-plate wave guides. Also draw attenu-
ation versus frequency characteristics of waves guided between parallel con-
ducting plates.
(b) A parallel plate wave guide made of two perfectly conducting infinite planes
spaced 3 cm apart in air operates at a frequency of 10 GHz. Find the maximum
time average power that can be propagated per unit width of the guide for
TE1 and TM1 modes. [8+8]
7. (a) Explain the different types of transmission lines. What are limitations to the
maximum power that they can handle.
(b) A coaxial limes with an outer diameter of 8 mm has 50 ohm characteristic
impedance. If the dielectric constant of the insulation is 1.60, calculate the
inner diameter.
(c) Describe the losses in transmission lines [8+4+4]
8. (a) Explain what is meant by voltage reflection coefficient in a transmission line
The voltage reflection coefficient due to load connected to a lossless transmis-
sion line of characteristic impedance 100
and working at 3 GHz is 0.5, 450.
Assuming the load voltage to be 10 V, calculate the r.m.s voltage and current
at intervals of one fourth wave length from the load up to a distance 5 cm.
(b) A 75
line is terminated by a load of 120 + j80
. Find the maximum and
minimum impedances on the line.
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