Exercise: Electromagnetic Field Theory

Questions for: Electromagnetic Field Theory

Find the radiation resistance of an antenna of length λ/10 meter?
A:
8 Ω
B:
780 Ω
C:
7.8 Ω
D:
78 Ω
Answer: C

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A wave is propagated in a waveguide at frequency of 9 GHz and separation is 2 cm between walls find cut off wavelength for dominant mode.
A:
4 cm
B:
1 cm
C:
2 cm
D:
8 cm
Answer: A

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The input impedance of short-circuited line of length l where λ/4 < l < λ/2, is
A:
resistive
B:
inductive
C:
capacitive
D:
none of the above
Answer: C

l < λ/4, ZL = 0

, if Zd comes +j kZC then inductive,

If Zd comes -j kZC then capacitive.

for 0 ≤ l ≤ 1/4, λ ≤ l ≤ 3λ/4 will be inductive.

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A broadside array operating at 100 cm wavelength consist of 4 half-wave dipoles spaced 50 cm apart. Each element carries radio frequency current in the same phase and of magnitude 0.5 A. The radiated power will be
A:
196 W
B:
73 W
C:
36.5 W
D:
18.25 W
Answer: A

P = n . I2 . Rr, where Rr = 80p2 Ω.

n = 4.

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The function f(x - vot) represent which of the following?
A:
A stationary wave
B:
A wave motion in forward direction
C:
A wave motion in reverse direction
D:
None of the above
Answer: B

f(x - vot) represents in +ve direction while f(x + vot) represents a progressive wave in -ve direction.

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