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
£ m V . ^ d) m V .ii)
A potential field is given by V » 3x2 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.
CS/B.Tech (ECE-NEW)/8EM-4/BC-404/07 4
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/e1 = 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. !
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 ■ ‘ ■ ■ ■ . A7‘ ‘ ‘ ■■■ ‘ – ‘ ✓ ‘ – .
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
CS/aYheh (BCS-iVEW)/8ra-4/BC-404/07 6
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
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 Z0 = 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 a2 respectively. 7