# 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) 10_ 9/f 36 re )                        b) 10 “ 19/( 36 n )

e) 0                                           d) l.

iv)         Which one is true for charge free region ?

a) V2(j)=l                           b) V2 (}) = 0

c) V 2 (j) = – —                       d) none of these.

r

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)     jz0 tan b) -jzQ tan (31

c) jz0 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) = co2 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

1. 2.    State and explain the following :

a)          Stoke’s theorem

b)          Helmholtz theorem.

1. 3.    Using Cartesian coordinates show that

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

1. 4.    Show that a lossless x/8 length line terminated as open circuit, behaves like a capacitor.
1. 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.

1. 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

1. 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

1. 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

1. 9.    a) State and explain Gauss’s law in differential form and
2. 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 = x2 + y2 + z2 and F = 2xya x + za + yz2 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.