EMTL
JNTUH BITS
SECTION-I: Multiple choice questions
Note:Don't think that these bots only will be repeated in mid exam.First through the last 4 units concepts well then solve the bits.These bits to cross check your knowledge
Note:Don't think that these bots only will be repeated in mid exam.First through the last 4 units concepts well then solve the bits.These bits to cross check your knowledge
1. For normal incidence of the wave on perfect
conductor [ b]
a) Surface current doesn’t exist b) surface exists
c) conducting current exiasts d) free charge exists on the
surface
2. A standing
wave [ d]
a) Progresses with less than light velocity b) progresses with
more than light velocity
c) progresses with equal to light velocity d) does not progress.
3. The range of
reflection coefficient is [ c]
a) 0 to 1 b) 0 to infinity c) -1 to 1 d) 1 to infinity
4. Electric and
magnetic fields which are parallel [d ]
a)Constitute power flow b) constitute infinite power flow
c)constitute unit magnitude power flow d) no power flow.
5. The
propagation velocity of TE waves [ a]
a)Depends on frequency b) independent of frequency
c) depends on square of frequency d) varies inversely with
frequency.
6. As per the boundary
condition, [b ]
a)The normal component of E is continuous across the boundary.
b)The tangential component of E is continuous across the
boundary.
c)The tangential component of D is continuous across the
boundary.
d)The normal component of H is continuous across the boundary
7. The magnetic field at the surface of
a good conductor is 2A/m. The frequency of the field is 600 MHz. The surface
r.m.s current density is [c
]
a)0.5 A/m b)0.5 A/m2 c)2 A/m d)2 A/m2
8. If the
reflection coefficient is -1/2 then the swr is [ d]
a)Zero b) one c)1/3 d) 3
9. The wave
impedance over the cross section of wave guide [d ]
a) Increases with frequency b) decreases with frequency
c) increases exponentially d) constant
10. Hysteresis
and eddy current losses in loading coils leads to [c ]
a) Increase in L b) Decrease in L c) Increase in R d) decrease
in R
1 1) Which
of these is not a correct form of the wave Ex = cos(ωt —βz)? [b ]
(a) Ex = cos(βz-ωt) (b) Ex = cos(ωt —βz-Π/2) (c) Ex = Re[ej(ωt
—βz)] (d) Ex = cos(2Πt/T-2Πz/λ)
12) What is the major factor for
determining whether a medium is free space, lossless dielectric, lossy
dielectric, or good conductor? [ c]
(a) Attenuation
constant (b) Constitutive parameters (σ,μ,ε)
(c) Loss tangent
(d) Reflection coefficient
13) In a certain
medium, E = 10 cos (108t — 3y) ax V/m. What type of medium is it? [ c]
(a) Free space
(b) Perfect dielectric (c) Lossless dielectric (d) Perfect conductor
14) For any
dielectric material ( σ/ωε) value is [a ]
a)<<1
b)>>1 c)=1 d)zero
15) Given that H
= 0.5 e-0.1xsin (106t- 2x) ay A/m, which of these statements are incorrect? [ b]
(a) α = 0.1 Np/m
(b)β = - 2 rad/m
(c) ω= 106rad/s
(d) The wave is polarized in the z-direction.
16) Which of the
following statements is not true of waves in general? [ a]
(a) It may be a
function of time only. (b) It may be sinusoidal or cosinusoidal.
(c) It must be a
function of time and space. (d) For practical reasons, it must be finite in
extent.
17) For a lossy
transmission line, the characteristic impedance does not depend on [ b]
(a) The operating
frequency of the line (b) The length of the line
(c) The load
terminating the line (d) The conductivity of the conductors
18) Which of the
following statements are not true of the line parameters R, L, G, and C? [c ]
(a) R and L are
series elements. (b) G and C are shunt elements.
(c)G = 1/R (d) LC
= με and RG = σε.
19) A lossless
transmission line of length 50 cm with L = 10 μH/m, C = 40 pF/m is operated
at 30 MHz. Its
electrical length is [c
]
(a) 20λ (b) 0.2λ
(c) 108° (d) 40Π
20) Ex = cos(ωt
+βz) represents a wave travelling in the __________________ [d ]
(a)-ve
x-direction (b)+ve x-direction (c)+ve z-direction (d)-ve z-direction
21. An electromagnetic
wave is to pass through an interface separating two media having dielectric
constants ε1
and ε2 respectively. If ε1 = 4ε2 , the
wave will be totally reflected if angle of incidence is [b ]
( a ) 00 ( b )
300 (
c ) 450 (
d ) 600
22. The Snell’s law of
refraction
23. The instantaneous rate
of energy flow per unit area at a point is [a ]
( a ) E x H ( b) ( c ) B
• ∇D • ∇( d ) ) (2 EHx∇∇
24. When electromagnetic
waves are reflected at an angle from a wall, their wavelength along the wall is
[ c]
( a ) shortened because of
the Doppler effect ( b) the same as in free space
( c ) greater than in the
actual direction of propagation
( d ) same as the
wavelength perpendicular to the wall
25. At the cut-off wave
length, the wave between the walls of parallel plane guide [d ]
( a ) is travel almost
parallel to the axis of the guide
( b ) is travel
perpendicular to the axis of the guide
( c ) is travel in zig-zag
path ( d ) has no wave motion
26. If the time dependence
of voltage is given as e-jwt, then Voe-γz will represent [ b]
( a ) forward travelling
wave (b ) backward travelling wave (c ) standing wave (d ) refracted wave
27. A lossless line of
length 500m has L=10μH/m and C=0.1pF/m at 1 MHz. The electrical length of the
line is
[ c]
( a ) 3600 ( b )
2700 (
c ) 1800 (
d ) 900
28. For an open circuited
line which is not true [b
]
( a ) Zin = -jZo cotβl ( b
) ( c ) 1 −= Γ l 1 = Γ l ( d ) S = ∞
29. Short-circuited stubs
are preferred to open-circuited stubs because the latter are [c ]
( a ) more difficult to
make and connect
( b ) made of a
transmission line with a different characteristic impedance
( c ) liable to radiate (
d ) incapable of giving a full range of reactances
30. For transmission-line
load matching over a range of frequencies, it is best to use a [c ]
(a) balun (b)
broadband directional coupler (c) double stub (d) single stub of adjustable
position
SECTION-II: Fill in the blanks
1. The frequency at which the wave motion ceases is
called Cutoff frequency.
2. A Lumped load line behaves as a Low pass filter
3. By inserting inductance in series with the line
to increase the inductance is called
Loading.
4. One neper is = 8.68 dB.
5. A short circuited λ/4 line can be used a Insulator
6. The range of UHF is 300 MHz to 3 Ghz
7. The loading practice is generally restricted to Cables only.
8. When a transmission line is shorted, the first
voltage minimum occurs at Load
9. The center of smith chart represents Matched load impedance.
10. Attenuation factor of TEM wave is proportional
to Square root. of frequency.
11.The relation between E and H in any medium is
____________
12) The value of intrinsic impedance of free space
is 377Ω
13) In a perfect dielectric medium attenuation
constant is Zero
14) The loss tangent value for a good conductor is ( σ/ωε)>>1
15) A wave propagating in a conducting medium attenuation constant and
phase constant values are_____________
16) The conductivity of silver is 3x106 mho/m.If
the skin depth is 1mm,find the frequency? 84.43kHz
17) Write the expression for reflection coefficient of a perfect dielectic
surface when the wave incident normal to the boundary.
TR =(η2-η1)/(η2+η1)
18) The Poynting vector physically denotes the power density
leaving or entering a given volume in a time-varying field
19) Brewster angle θB when the wave is parallally polarized
is
20) Critical angle θc for the total internal
reflection is 
21. An electromagnetic wave is incident at air-conductor
interface. If impedance of the conductor is 120π, the ratio of transmitted and
incident electric fields is 2
22. The critical angle for a wave propagating from Teflon (
εr=4) into free space is 30˚
23. The orientation of the electric field with respect to
the plane of incidence determines Polarization
of a wave at the interface between two different regions.
24. When the free-space wavelength of a signal equals the
cutoff wavelength of the guide, the phase velocity of the signal becomes infinite
25. The wave impedances for waves between parallel planes
are functions of frequency
26. A line is of a length ‘l’ has characteristic impedance
‘Zo’. The line is cut into half. The value of characteristic impedance becomes Zo
27. Impedance inversion may be obtained with Quarter wave line
28. The velocity factor of a transmission line depends
on the dielectric
constant of the material used
29. In a transmission line, the attenuation is
given as 0.3dB/km. After 10km the power will be 0.5 of input power
30. In electromagnetic waves, polarization is due
to the transverse nature of the waves
Prepared By
Mukesh