Electromagnetic theory miscellaneous Easy Questions and Answers | Page - 10

Electromagnetic theory miscellaneous

A transmitter radiates power of 20 kW and its base current is 18 A. The radiation resistance of the antenna is—

1. 1111 Ω
1. 900 Ω
1. 75 Ω
1. 62 Ω

View Hint View Answer Discuss in Forum

Power radiated = 20 kW = 20 × 10³ W and we have basic relation of antenna that is I² R_r = Power radiated
R_r =
W =
20 × 10³ = 61.6 Ω
l² 18 × 8

Correct Option: D

Power radiated = 20 kW = 20 × 10³ W and we have basic relation of antenna that is I² R_r = Power radiated
R_r =
W =
20 × 10³ = 61.6 Ω
l² 18 × 8

The Q of a antenna in loaded and unloaded condition is related to—

1. Q_loaded = 2 Q_unloaded
1. Q_loaded = 1 Q_unloaded
  2
1. Q_loaded = Q_unloaded
1. Q_loaded = 1 Q_unloaded
  3

View Hint View Answer Discuss in Forum

NA

Correct Option: D

NA

The main difference between operation of a transmission lines and waveguide is that—

1. The latter are not distributed like transmission line
1. The former can use stubs and quarter wave transformers unlike the latter
1. Transmission lines use the principal mode of propagation and, therefore, don't suffer from low frequency cut-off
1. Terms such as impedance matching and standing wave ratio can't be applied to waveguide

View Hint View Answer Discuss in Forum

Transmission line does not suffer from cut-off frequency because wave travels in principle mode of operation. On other hand waveguide suffers from such problem.

Correct Option: C

Transmission line does not suffer from cut-off frequency because wave travels in principle mode of operation. On other hand waveguide suffers from such problem.

A line with lumped parameters of 10 T sections series resistances of 10 ohms per section and 200 ohms shunt resistance is matched to a generator with emf of 3 volts and terminated by its characteristic impedance. The characteristic impedance is given by—

1. 45 Ω
1. 22.4 Ω
1. 90 Ω
1. 180 Ω

View Hint View Answer Discuss in Forum

Characteristic impedance of line of T section may be calculated from the image impedance and it is given by
Z_C =
√ Z₁ + Z₂
Z²₁
4

so we get Z_C = 45 Ω and its value remains same for any number of symmetric sections.

Correct Option: A

Characteristic impedance of line of T section may be calculated from the image impedance and it is given by
Z_C =
√ Z₁ + Z₂
Z²₁
4

so we get Z_C = 45 Ω and its value remains same for any number of symmetric sections.

A (75 – j 50) Ω load is connected to coaxial transmission line of Z₀ = 75 Ω at 10 GHz the best method of matching consists in connecting—

1. A short circuited stub at the load
1. An inductance at the load
1. A capacitance at some specific distance from the load
1. A short circuited stub at some specific distance from the load

View Hint View Answer Discuss in Forum

Best method of matching the load given by 75 –j 50 is to connect the stub which is short circuited at some distance here less than λ/4.

Correct Option: D

Best method of matching the load given by 75 –j 50 is to connect the stub which is short circuited at some distance here less than λ/4.