# WBUT Question Papers CS

## Electromagnetic Waves And Radiating Systems B Tech Sem Forth

Group – A ( Multiple Choice Type Questions)

Choose the correct alternatives for any ten of the following : 10×1 = 10

i) The magnetic flux density if and vector potential ^ are related as

a) f=Vx^ b) ^ = V

c)

£ m V . ^ d) m V .ii)

A potential field is given by V » 3x^{2} y – yz. The electric Add at P (

2, -1, 4 ) is

a) 12?- 8? V/m b) 12?-? V/m

c) 12″? + 8? + 1c V/m d) – 12? – 8? – 7c V/m.

ill) The electric field lines & equlpotentlal lines

a) are parallel to each other

b) are one and the same

c) cut each other orthogonally

d) can be inclined to each other at any angle.

‘ . . . ■ x ■ ‘ ■

iv) A transmission line of length ^ shorted at far end behaves like

£0 series resonant circuit b) parallel resonant circuit

c) pure inductor d) pure capacitor.

v) Maxwell’s equation V x it * + T$ represents

a) Gauss’s law in magnetism

b) KirchhofFs current law for direct current

c) Biot-Savart law

d) Generalized Ampere’s circuital law.

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vi) In a two region system, a plane waveis arriving at a normal ineMence in air with _{f} ff amplitude E j |* 100 V/m and frequency 100 MHz. The sigh is Teflon ( e _{r} = 2-1,

e ^{11}/e^{1} = 0 ). The amplitude of the reflected wave is

a) 18-34 V/m b) 36-68 V/m

c) – 18-34 V/m d) – 36-68 V/m. f

vii) If the frequency of the incident wave? increases by a factor of 4, the depth to which a wave penetrates a conducting material ‘

a) increases by a factor of 2 ^{!} b) increases by a factor of 4 c) decreases by a factor of 2 d) decreases by a factor of 4.

viii) The MUF of transmission between two stations 500 km apart at f _{crit} = 9 MHz and minimum value of incident angle i = 45° is

a) 0*7 MHz b) 25-4 MHz

12-7 MHz , d) 18 1®z. V |

ft) A quarter-wave monopole antenna operating in air at a frequncy of 1 MHz must have an overall length (I) of

a) l»X b) 150 m

c) 75 m d) I«X.

i ’ ■ ■ ■ ‘ .i- ■ ■

x) The radiation resistance of a dipole, having a length of 4 cm, radiating 50 W of

power at a frequency of 500 MHz is

a) 3-5 Q b) 0-82 £2

c) 1-75 0 i d) 7-0 Q . 1

xi) Ohm’s law is obeyed by

aj conduction current b) convection current c) conduction & convection current d) none of these.

■ ‘ ■ . … . ■ * ■ -V’ ■ . ‘

xii) The direction of propagation of EM wave is obtained from

a) E x H b) E . H

^{1} . _{:} ; • •. . ■ ■- . • ■ ^{1} ■ “

c) E d) H. !

j 24806-ffVHr

a

Group – B (Short Answer Type Questions)

– .. _{;}*r -■ ■ • ‘ . ■

Answer any three questions. 3 x 5 = 15

- Define the term ij VSWR and ii) ‘Reflection co-efficient’ for transmission’line.

Explain the relationship between them.

- Prove that V x it = if + . The symbols have usual meaning.
- A 2m long lossless transmission line has an impedance of 300£l . The velocity of propagation is 2-5 x 10
^{s}m/s. The load has an impedance of 300Q with sending end voltage being 60V at 100 MHz. Find :

a) The phase constant * .

b) The load voltage ,

‘ i ■ ‘ ■ ■ ■ . A^{7}‘ ‘ ‘ ■■■ ‘ – ‘ ✓ ‘ – .

c) The load current

d) The load reflection coefficient &

e) Standing wave ratio.

- Why is ionosphere important for radiowave propagation ? Describe the different layers of ionosphere.
- What do you mesm by magnetic vector potential ? Write down the Maxwell’s equations for timp varying electromagnetic fields, when the medium is lossless, linear, isotropic, homogeneous and source free. 3 + 2

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Group – C (Loag Answer Type Questions)

Answer any three questions. 3 x 15 = 45

- a) Find the expression of Radiation resistance of a short electric dipole with

uniform current distribution. ^{7}

b) Define complex Poynting vector. 3

<4 Explain the concept of skin depth & find out an expression for that. 5

- a) Derive an expression for the input impedance of a lossless transmission line,

in terms of relevant parameters, when the line is terminated in load impedance

7 6

b) Show that for a lossless transmission line the impedance of a line repeats over every j distance. 5

c) A transmission line with air as dielectric has Z_{0} = 50Q and a phase constant of 3 rad/m at 10 MHz. Find the inductance & capacitance of the line. 4

- a) What is electromagnetic interference ? 2

b) Why does the short wave radio signal propagate with very low attenuation at night ? Describe the sky-wave propagation of EM waves. 3 + 6

c) What is fading ? Briefly describe the diversity techniques to reduce the effect of fading. 1+3

- a) Obtain the Poynting theorem for the conservation of energy in an electromagnetic

field and discuss the physical significance of each term in resulting equation. 6

b) In free space E (z, t) = 50 cos (tot-fiz) V/m. Find the average power crossing a circular area of radius 5m in the plane x = constant. 5

c) Derive the equation of continuity for time varying fields. 4

- a) State & explain Faraday’s law. 4

bj Derive the induced emf when a stationary loop is in the time varying B fields. 4

c) Determine the magnetic field intensity at a point P due to a current carrying filamentary conductor AB carrying current I along Z axis with its upper and lower ends subtending angles a, and a_{2} respectively. 7

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