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EC English
Subject : EMFT HOMEWORK
Chapter : Transmission Line
Topic : Lossless and Distortion Less
1. Two coaxial cables 1 and 2 are filled with different (b) must be a distortion less line.
dielectric constants εr1 and εr2 respectively. The ratio of (c) may not be a lossless line.
the wavelengths in the two cables, (λ1/λ2) is (d) may not be a distortion less line.
(a) r1 / r 2 (b) r 2 / r1
(c) r1 / r 2 (d) r 2 / r1 7. In air, a lossless transmission line of length 50 cm with
L = 10μH/m, C = 40pF/m is operated at 25MHz. Its
electrical path length is
2. The capacitance per unit length and the characteristic (a) 0.5 meters (b) λ meters
impedance of a lossless transmission line are C and Z0
(c) π/2 radians (d) 180 degrees
respectively. The velocity of a travelling wave on the
transmission line is
8. A coaxial cable with an inner diameter of 1 mm and
(a) Z0C (b) 1/(Z0C)
outer diameter of 2.4 mm is filled with a dielectric of
(c) Z0/C (d) C/Z0
relative permittivity 10.89. Given 0 = 4 × 10–7H/m,
10−9
3. A transmission line is distortion less if 0 = F / m, the characteristic impedance of the
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(a) RL = (b) RL = GC cable is
GC
(a) 330 Ω (b) 100 Ω
(c) LG = RC (d) RG = LC
(c) 143.3 Ω (d) 15.92 Ω
4. A transmission line has a characteristic impedance of
9. For a parallel plate transmission line, let V be the speed
50Ω and a resistance of 0.1Ω/m. If the line is distortion
of propagation and Z be the characteristic impedance.
less, the attenuation constant (in Np/m) is
Neglecting fringe effects, a reduction of the spacing
(a) 500 (b) 5 between the plates by a factor of two results in
(c) 0.014 (d) 0.002 (a) halving of V and no change in Z.
(b) no changes in V and halving of Z.
5. A transmission line of characteristic impedance 50Ω is (c) no change in both V and Z.
terminated by a 50Ω load. When excited by a
(d) halving of both V and Z.
sinusoidal voltage source at 10GHz, the phase
difference between two points spaced 2 mm apart on
the line is found to be π/4 radians. The phase velocity 10. The characteristic impedance of a transmission line
of the wave along the line is with inductance 0.294 μH/m and capacitance 60 pF/m,
is
(a) 0.8 × 108 m/s (b) 1.2 × 108 m/s
(a) 49Ω (b) 60Ω
(c) 1.6 × 108 m/s (d) 3 × 108 m/s
(c) 70Ω (d) 140Ω
6. A transmission line whose characteristic impedance is
a pure resistance 11. For a transmission line with homogeneous dielectric,
the capacitance per unit length is 'C', the relative
(a) must be a lossless line.
2
permittivity of the dielectric is εr and velocity of light j0) Ω at ω =106 rads–1. The values of the line constants
in free space is 'v'. The characteristic impedance Z0 is L, C, R, G are, respectively,
equal to (a) L = 200μH/m, C = 0.1μF/m, R = 50Ω/m, G = 0.02
r r S/m
(a) (b)
vC vC (b) L = 250μH/m, C = 0.1μF/m, R = 100 Ω/m, G =
0.04 S/m
r r
(c) (d) (c) L = 200μH/m, C = 0.2μF/m, R = 100 Ω/m, G =
vC vC
0.02 S/m
(d) L = 250μH/m, C = 0.2μF/m, R = 50 Ω/m, G = 0.04
12. What is the attenuation constant α for distortion less S/m
transmission line?
C
(a) = 0 (b) = R 15. Conditions for a transmission line to be of low loss are
L
(a) R >> L, G >> C
(c) =R
L
(d) =
RL (b) R << L, G >> C
C C
(c) R << L, G << C
(d) R >> L, G << C
13. A 50Ω distortion less transmission line has a
capacitance of 10–10 F/m. What is the inductance per
16. A Lossy transmission line has resistance per unit
meter?
Length R = 0.05Ω/m. The line is distortion less and has
(a) 0.25 µH (b) 500 µH
characteristic impedance of 50Ω. The attenuation
(c) 5000 µH (d) 50 µH constant (in Np/m correct to three decimal places) of
the line is_________________.
14. The propagation constant of a lossy transmission line is
(2 + j5) m–1 and its characteristic impedance is (50 +
3
Answer Key
1. (b) 9. (b)
2. (b) 10. (c)
3. (c) 11. (c)
4. (d) 12. (b)
5. (c) 13. (a)
6. (b) 14. (b)
7. (c) 15. (c)
8. (d) 16. (0.001)
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