# WBUT Previous Years Question Papers EE

## Field Theory B Tech 3rd Sem 2011-12

Time Allotted : 3 Hours

The figures in the margin indicate fuR marks.

Candidates are required to give their answers in their own words

as far as practicable.

f

GROUP – A ( Multiple Choice Type Questions )

1. Choose the correct alternatives for any ten of the following :

10 x 1 = 10

1) The intrinsic impedance of free space is given by a) 333 £2

b) 377 £2

^{c) }^{4n n} ‘ d) 2n Q .

ii) Minimum value of VSWR is

f*

a) – b) – 2

^{c) 0} d) 1.

iii) € _{Q} for vacuum is given by

a) ^{1}0^{_ 9}/f 36 re ) b) 10 “ ^{19}/( 36 n )

e) 0 d) l.

iv) Which one is true for charge free region ?

a) V^{2}(j)=l b) V^{2} (}) = 0

■

c) V ^{2} (j) = – — d) none of these.

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v) Which one is conservation of charge equation for the steady currents ?

a) V-J = 1 b) V-J = 0

c) V-J = 471 d) V-J = p

vi) Lorentz force for a point charge in motion in external electric and magnetic field is given by

a) F = Q ( E + ux B ) –

b) F=Q(B+ uxH)

9

f

c) F = 9 ( H + uB )

d) F= Q [E + uB).

vii) Which of the following can be the unit of emf ?

a) Wb/s b) Wb/v

c) v/s d) s/v.

a) TEM b) quasi TEM

c) TE d) TM.

ix) For a lossless transmission line the characteristic impedance is given by

VT » VF **‘**

c) 271 d) 271

x) For a lossless transmission line terminated with a short

circuit, the i/ p impedance is given by ( for line characteristic impedance z _{0} )

a) jz_{0} tan b) -jz_{Q} tan (31

c) jz_{0} cot pi d) -jz _{0} cot (3J .

xi) Wave number is given by

a)

k – a) V |i€ b) k- 2n V|Lie

c)

k = Vjxe d) = co^{2} jig .

a) 8 = V2/( ©jxa )

b) 5 = V7r/( cofia )

c) 5 = 2/V( copa |

d) 8 = rc/V ( a)(aa I .

GROUP -B ( Short Answer Type Questions )

Answer any three of the following. 3×5= 15

*2.*State and explain the following :

a) Stoke’s theorem

b) Helmholtz theorem.

*3.*Using Cartesian coordinates show that

V-( V xA) = 0 and V x ( V<J> ) = 0.

*4.*Show that a lossless x/8 length line terminated as open circuit, behaves like a capacitor.

*5.*a) Derive an expression for the wave equation in terms of

electric field intensity in a perfect dielectric of permittivity e, permeability |i for the medium with no absorption.

b) For a lossy dielectric |li _{r} = 1, e _{r} = 48, a = 20 S/m,

calculate the attenuation constant and phase constant at frequency of 16 GHz.

*6.*Deduce boundary conditions on electric vector £? and L? for

Dielectric-Dielectric interface.

GROUP -C ( Long Answer Type Questions )

Answer any three of the following. 3 x 15 = 45

*7.*a) What is polarization ? How will you generate right

handed circular polarize waves using linearly polarized wave sources ? Define axial ratio. 2 + 2 + 2

b) State and prove Poynting Theorem. 9

*8.*a) Draw the equivalent circuit of a transmission line. What

is distortionless line ? How to achieve distortionless

condition on the line ? Derive necessary conditions.

2 + 2 + 5

b) Find the characteristic impedence, propagation constant and velocity of propagation for a transmition line having the following parameters :

R = 84 ohm/km, G = 10″ ^{6} mho(m,L = 0 01H/km, C = 0 061 fiF/km, frequency = 1000 Hz. 6

*9.*a) State and explain Gauss’s law in differential form and- explain what do you mean by div. D. 7

b) A circular disc of radius a’ is situated in the xy plane at

Z = 0, with its centre at the origin charge density on disc is p _{s} = constant c/m ^{2} . Calculate the field at any

point ( 0, 0, h ) in cylindrical co-ordinate system. 8

*10. *Fine the Gradient of a function G at the point ( 4, 5, 6 ) and Divergence of Fat { 3, 2, 1 ), given that

G = x^{2} + y^{2} + z^{2} and F = 2xya _{x} + za + yz^{2} a .

y z

Given point P ( 1. 2, 3 ). Express P in cylindrical and spherical co-ordinates. _{9 + 6}

Write short notes on any three of the following :

**a) **Magnetic material

**b) **Poisson’s and Laplace’s equation

**c) **Maxwell’s equations

**d) **Propagation constants

**e) **Biot-Savart law.