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Posted By: jothi vignesh Member Level: Gold Posted Date: 07 Jul 2008
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2005 Anna University B.E ELECTROMAGNETICS AND RADIATION Question paper
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Code: A - 14 Subject: ELECTROMAGNETICS AND RADIATION
Time: 3 Hours Max. Marks: 100
NOTE: There are 11 Questions in all.
Question 1 is compulsory and carries 16 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.
Answer any THREE Questions each from Part I and Part II. Each of these questions carries 14 marks.
Any required data not explicitly given, may be suitably assumed and stated
Q.1 Choose the correct or best alternative in the following: (2x8)
a. A ball having charge 'q' floats in mid air, in presence of a line charge having linear charge density . If the distance of the ball from the charge is 'd' then the mass of the ball is
(A) (B)
(C) (D)
b. A positive charged pendulum is oscillating in a uniform electric field (Fig.1).
Its time period as compared to that when it was uncharged :
(A) will increase.
(B) will decrease.
(C) will not change.
(D) will first increase and then decrease.
c. The equivalent capacitance between A and B (Fig.2) is
(A) 2 C. (B) 3 C.
(C) 4 C. (D) .
d. An electron moves straight inside a charged parallel plate capacitor of uniform surface charge density (Fig.3). The space between the plates is filled with constant magnetic field of induction . Neglect gravity, the time of straight line motion of the electron in the capacitor is
(A) (B)
(C) (D)
1
Index Next>>e. In a two region system, a plane wave is arriving at normal incidence in air with amplitude and frequency The slab is teflon . The amplitude of the reflected wave is:
(A) 18.34 v/m. (B) -18.34 v/m.
(C) 36.68 v/m. (D) -36.68 v/m.
f. The lower cut-off frequency of a rectangular waveguide with inside dimensions operating at 9 GHz is
(A) 3.8 GHz. (B) 9 GHz.
(C) 7.6 GHz. (D) None of the above.
g. The radiation resistance of a dipole having length 4 cm, radiating 50 W of power at a frequency of 500 MHz is
(A) 3.5 . (B) 0.82 approx.
(C) 1.75 . (D) 7 .
h. The MUF of transmission between two stations 500 Km apart at and minimum value of incident angle is
(A) 0.7 MHz. (B) 25.4 MHz.
(C) 12.7 MHz. (D) 18 MHz.
PART I
Answer any THREE Questions. Each question carries 14 marks.
Q.2 a. Three very large metal plates are given charges as shown (Fig.4). Find out the final charge distribution. Assume the cross-sectional area of each plate to be 'A'. (7)
b.
A particle of mass 40 mg and carrying a charge 5x10-9 C is moving directly towards a fixed positive point charge of magnitude 10-8 C. When it is at a distance of 10 cm from the fixed positive point charge, it has a velocity of 50 cm/sec. At what distance from the fixed point charge will the particle come momentarily at rest ? (7)
Q.3 a. Find the capacitance of an isolated ball-shaped conductor of radius R1 surrounded by an adjacent concentric layer of dielectric with permittivity K and outer radius R2. (7)
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<>b. Fig. 5, shows a parallel plate capacitor with plates of width 'b' and length ' '. The separation between the plates is 'd' . The plates are rigidly clamped and connected to a battery of emf V. A dielectric slab of thickness 'd' and dielectric constant 'K' is slowly inserted between the plates. Calculate the energy of the system when the length 'x' of the slab is introduced into the capacitor. (7)
Q.4 a. Define "Biot-Savart Law" and discuss its significance. (4)
b. A square frame carrying a current I=0.9 A is located in the same plane as a long straight wire carrying a current I0=5.0A (Fig.6). The frame side has a length a=8.0 cm. The axis of the frame passing through the midpoints of the opposite sides is parallel to the wire and is separated from it by the distance which is n = 15 times greater than the side of the frame. Find:
(i) Ampere force acting on the frame.
(ii) The mechanical work to be performed in order to turn the frame through about its axis with the currents maintained constant. (10)
Q.5 a. Write down Maxwell's equations in charge free and non-conducting medium and hence derive the wave equations of the electric and magnetic fields in the differential form. (7)
b. Consider a wave, which is propagating in a medium having as permeability and as the permittivity. Find the ratio of the electric and magnetic field. (7)
3
<>Q.6 Consider a plane wave travelling along x direction incident normally on the boundary parallel to x = 0 plane. Assume the boundary as perfect dielectric material. Derive equations which define reflection and transmission coefficients in terms of impedances of the two media for both electric and magnetic fields. (14)
PART I
Answer any THREE Questions. Each question carries 14 marks.
Q.7 a What are the major sources of losses in R.F. transmission Lines? To what extent it would be justified to assume R.F. transmission Lines to be lossless? Derive expressions for Attenuation Constant and Phase Shift Constant for lossless transmission Lines. (10)
b. A transmission Line is to be matched to a antenna with a piece of transmission Line. If the operating frequency is 100 MHz, calculate the length of the line required and also the characteristic impedance of the line from which it is to cut. (4)
Q.8 a. What do you understand by waveguide modes? What are dominant modes? Sketch rectangular wave guide mode field configuration for TE10 and TM11 mode. (4)
b. Show that a 1GHz signal cannot propagate TE10 in the mode in a rectangular waveguide having a wall separation of 5 cm. (5+4)
Q.9 What is broad side array? For the case of the broad side array, derive expression for the following :
(i) the total radiated field in the far region.
(ii) condition for principal maxima.
(iii) conditions for nulls and secondary maxima.
(iv) width of the principal lobe. (14)
Q.10 a. What do you understand by ground wave propagation? Discuss in detail with the expressions for cross over frequency (fco), electric field at a distance 'd' and the loss factor. (7)
b. Estimate the electric field strength at d = 50 Km from a short vertical monopole radiating over ground with mean conductivity (7)
Q.11 Write short notes on any TWO of the following : (2 x 7)
(i) Smith Chart and its applications.
(ii) Cavity resonator.
(iii) Boundary conditions for electric and magnetic fields.
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