# WBUT Question Papers EC

## Electromagnetic Waves And Radiating System B Tech Sem Forth 2010

Time Allotted : 3 Hours

Full Marks: 70

The figures in the margin indicate Jidl marks.

Candidates are required to give their answers in their own words

as far as practicable.

GROUP – A (Multiple Choice Type Questions)

1. Choose the correct alternatives for the following :

10 x 1> 10

I) Which of the following is zero ?

a)   Grad div A   b) dlv gradient V

c) . div curl A     d) Curl curl A.

UO Maxwell’s equation Curl H = J + 6 D/8 t represents

a)        / Magnetic vector potential A . b) Gauss’law in magnetism

c)            Generalised Ampere’s circuital law

d)            Biot-Savart law.       /

w) a transmission line is called a distortionless line when

a)    R/b – G/C b) R/G=C/L

c)  RG = L/C            d) R/G = LC.

 ty) Tire Intrinsic wave impedance of a medium with permeability and permittivity e is

v)            Which of the following layers persists at night ?

a)            D layer             b) E layer

c)   FI layer    d) F2 layer.

vi)           For a good plane conductor, skin depth varies

a)            directly as square root of frequency

b) inversely as square root of frequency

c)            directely as a function of frequency

d)           inversely with frequency.

vii)
Pqynting vector for EM wave has unit

b)   W/m2

d)            (W/m)2.

viii)       The direction of propagation of electromagnetic wave is obtained from

 a) ExH <4 E
 b) E-H d) E/H.

ix)          Ohm’s law is obeyed      ,

a)            conduction current

b)            convection current

c)    conduction current and convection current

d)           none of these.

x)             Hertz dipole is a dipole with length

 a) X/2 c) 31/4
 b) X/4 d) X/6.

GROUP – B (Short Answer Type Questions)

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

1. Establish the relation, VxH = J+ 8D/8t, where symbols have their usual meanings                           ^
2. Define the following terms : .

a)            VSWR

b)           Reflection,co-efficient for transmission line.

1. Explain the concept of skin depth and find Out an expression for that.
2. Derive the relation between antenna aperture and effective height of *an antenna.                        2 + 3
3. a) What is Smith chart ? What are the various applications

of Smith chart in transmission line ?

b)           Define. characteristic impedance of lossless transmission line.                                     3 + 2

GROUP – C (Long Answer Type Questions )

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

1. a) Write down Maxwell’s equations for time varying

electromagnetic fields : when the media are homogeneous, source-free, loss-less, isotropic and linear.

b)           Obtain an expression of; wave equation of a conducting medium.                           .

c)            What do you mean by perfect conductor ?

d)           Explain Maxwell’s fourth equation of modified Ampere’s circuital law. What is displacement current ?

4 + 4 + 2 + 5

1. a) Obtain Poynting theorem for conservatism of energy in

an electromagnetic field arid discuss the physical significance of each term in resulting equation.

b) Explain boundary conditions for an interface separating

dielectric e _ and dielectric e , . 10 + 5

1. a) Find an expression of radiation resistance of a short

electric dipole with uniform current distribution,

b)             Derive an expression for the input impedence of Zin of . a lossless transmission line in terms of relevant

parameters when the line is terminated in load impedance of Z,.                                     8+7

1. a) How does sky wave prop£^ation take place ?
2. b)   Explain skip-distance and virtual height in sky wave.

c)           Explain the difference between critical frequency and MUF.  3×5

1. Write short notes on any three of the following :  3×5

a)            Yagi-Uda antenna

b)            Quarter waveiength transmission line

c)             Half wave dipole antenna

■’ • ’ • ( ■

d)            Boundeiy condition of magnetic field

e)             MUF.