Electronics and Communication Engineering - Electromagnetic Field Theory

6. 

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: Option C

Explanation:

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.


7. 

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: Option A

Explanation:

.


8. 

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: Option C

Explanation:

.


9. 

Charge needed within a unit sphere centred at the origin for producing a potential field,

A. 12 pc
B. 60 pc
C. 120 pc
D. 180 pc

Answer: Option C

Explanation:

q = 120p coulomb, r = 1 meter.


10. 

A rectangular metal waveguide filled with a dielectric of relative permittivity εr = 4, has the inside dimensions 3 x 1.2 cm, the cut off frequency for the dominant mode is

A. 2.5 GHz
B. 5 GHz
C. 10 GHz
D. 12.5 GHz

Answer: Option B

Explanation:

for dominant mode.