Which of the following should dominant wave have? Lowest cut off frequency Highe

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Question
Which of the following should dominant wave have?
Options
A. Lowest cut off frequency
B. Highest cut off frequency
C. No attenuation
D. No phase shift

Correct Answer

Lowest cut off frequency

Explanation

Lowest cut off frequency or highest wave-length in a waveguide gives dominant modes.

Electromagnetic Field Theory problems

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1. A short circuited stub is shunt connected to a transmission line as shown in the figure is, if z₀ = 500 ohms, the admittance y seen at the function of the stub and the transmission line is
Options
A. (0.01 - j 0.02) mho
B. (0.02 - j 0.01) mho
C. (0.04 - j 0.02) mho
D. (0.02 + j 0) mho

2. Refractive index of glass is 1.5. Find the wavelength of a beam of light with a frequency of 10¹⁴ Hz in glass. Assume velocity of light is 3 x 10⁸ m/sec in vacuum.
Options
A. 4 ?m
B. 3 ?m
C. 2 ?m
D. 1 ?m

3. Find the noise factor for an antenna at 27�C with equivalent noise temperature 30�K
Options
A. 20
B. 100
C. 300
D. 1.1

4. A plane electromagnetic wave travels in dielectric medium of relative permittivity 9. Relative to free space, the velocity of propagation in the dielectric is
Options
A. increased by a factor of 9
B. increased by a factor of 3
C. unchanged
D. reduced by a factor of 1/3

5. A hollow rectangular waveguide has dimensions a = 2b. Calculate the amount of attenuation, if the frequency is 3 GHz, and b = 1 cm.
Options
A. 49
B. 47.33
C. 50.33
D. 50

6. The torque (in mm) acting on a circular current loop of radius 1 mm in the xy plane, connected at the origin and with current 0.1 A, flowing in the sense of increasing in a magnetic field
is
Options
A.
B.
C. 10^-12p
D. - 10^-12p

7. Calculate the wave impedance for TM mode in rectangular waveguide for dominant mode at 3 GHz having
Options
A. (120p) ?
B. 377 ?
C. 226 ?
D. 629 ?

8. Characteristic impedance of a transmission line is 50 ?. Input impedance of the open circuited line.
Z_oc = 100 + J150 ?. When transmission line is short circuited, then value of the input impedance will be
Options
A. 50 ?
B. 100 + J150 ?
C. 7.69 + J11.54?
D. 7.69 - J11.54 ?

9. The input impedance of short-circuited line of length l where ?/4 < l < ?/2, is
Options
A. resistive
B. inductive
C. capacitive
D. none of the above

10. Z_L = 200 ? and it is desired that Z_i = 50 ? The quarter wave transformer should have a characteristic impedance of
Options
A. 100 ?
B. 40 ?
C. 10000 ?
D. 4 ?

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