Mumbai University Previous year question papers
V Sem Electronics Examination May 2006
N.B.: (1) Question No.1 is compulsory.
(2) Attempt any four questions out of remaining six questions.
(3) Ftgtlres to the right indicate ful.1marks.
(4) Vector notation should be used wherever necessary.
(5) Assumptions made should be clearly sta1ed.
(6) Assume any suitable data whenever required but justit’y the same.
1. Answer any foul’ from the following :-
(a) Prove that V. is = Pvand obtain Laplace’s and Poisson’s eqauation
(b) Explair the significance of displacement current
(c) What is skin effect? Define skin depth and state hew is it related to the attenuation constant
(d) Briefly explain the concept of retarded potentials.
(e) Write a short note on Smith chart
(f) What is uniform plane wave? Explain what is mea.nt by transverse electromagnetic wave.
2. (a) State Maxwell’s equations j’or static .fields. Explain how are th~3Ymodified for ti11evarying fields.
(b) The field intensity E= 250 sin 1010t (VIm) for a field ‘propagating in the medium whose cr = 5slm andEr = 1. Calculate the displacement current density 3D, the conducticn current density Jc and the frequency at which Jc=JD. 8
3. (a). State and explain Poynting vector using modified Ampere’s law derive the Poynting theorem and describe thE!significance of each of its terms.
(b) Consider a circular cylinder with radius of one meter and length 0.75 m in free f;pace with its axis along the z direction. An EMwave is propagating in this positive z direction wi1:hits electric field E= ili [2~f(t -~)lax(vjm) Where f = 100 MHz and c is the velocity of light. Determine (i) Poynting vector and (ii) Net power flow enterin9 the cylinder.
4. (a) Derive the boundary conditions for electric and magentic fj~)ldvectors at the boundary of two dielectric media.
(b) An electromagnetic wave propagates in free space. Its fields arE! given by :
E=30 7[ ej (s1081 + pz) atx (VIm)
H = Ho ej (10 1+ ~z)ay (AIm)
Find Ho and 13.
5.(a) Derive the expressions for tl,e reflection coefficient and transmise;ion coefficient br perpendicularly polorized plane wave incidE!nt obliquely on a perfect conductor.
(b) A plane wave of 200 MHz travelling in free space impinges normally on a large block of material having Er = 4, ~r = 9 and cr= O. Determine ’11’ ‘1.’2’131,I).” TTand TR’ 6. (a) Derive an expression for the characteristic impedance of a two wire transmission line.
6. A loss less 50 Q transmission line is terminated in 25 + j 50 Q. Find (a) voltage ref ection coefficient;
(b) current reflection coefficient;
(c) VSWR and (d) impedance at 0.3 ‘A.distance from the load.
7.Explain briefly the radiation for a short dipole in free space. Show that the power radiated hy the short dipole.
p=80 7[2 12 rms (dl/’A.)2
Hence obtain the expression for radiation resistance