Test: Power & Poynting Vector - Electronics and Communication Engineering (ECE) MCQ

Answer: b
Explanation: The Poynting vector gives the power of an EM wave. Thus P = EH/2. On substituting for E = 12 and H = 15, we get P = 12 x 15/2 = 90 units.

Answer: c
Explanation: The power of a wave is given by P = V²/2Zo, where V is the generator voltage and Zo is the characteristic impedance. on substituting the given data, we get P = 140²/(2×50) = 196 units.

Answer: d
Explanation: The fraction of the reflected to the incident power is given by the reflection coefficient. Thus Pref = R²xPinc. On substituting the given data, we get Pref = 0.5² x 16 = 4 units.

Answer: a
Explanation: The fraction of the transmitted to the incident power is given by the reflection coefficient. Thus Pref = (1-R²) Pinc. On substituting the given data, we get Pref = (1- 0.5²) x 16 = 12 units. In other words, it is the remaining power after reflection.

Answer: b
Explanation: The ratio of the reflected to the incident voltage is the reflection coefficient. It is given by R = 5/15 = 1/3. To get the transmission coefficient, T = 1 – R = 1 – 1/3 = 2/3.

Answer: d
Explanation: The voltage reflection coefficient is the negative of the current reflection coefficient. For a current reflection coefficient of -0.75, the voltage reflection coefficient will be 0.75.

Answer: a
Explanation: The attenuation refers to the power loss. Thus the power loss is given by 20 units. The power loss in dB will be 10 log 20 = 13.01 decibel.

Answer: c
Explanation: The return loss is given by RL = -20log R, where is the reflection coefficient. It is given as 0.5. Thus the return loss will be RL = -20 log 0.5 = 6.02 decibel.

Answer: a
Explanation: The power of an antenna is given by Prad = Ia² Rrad, where Ia is the antenna current and Rrad is the radiation resistance. On substituting the given data, we get Rrad = Prad/Ia² = 120/5² = 4.8 ohm.

Answer: a
Explanation: The transmission coefficient is the reverse of the reflection coefficient, i.e, T + R = 1. When T = 0.65, we get R = 0.35. Thus the return loss RL = -20log R = -20log 0.35 = 9.11 decibel.

Answer: c
Explanation: The return loss is given by RL = -20log R. The reflection coefficient can be calculated as R = 10^(-RL/20), by anti logarithm property. For the given return loss RL = 12, we get R = 10^(-12/20) = 0.25.

Answer: a
Explanation: The return loss is given by RL = -20log R. The reflection coefficient can be calculated as R = 10^(-RL/20), by anti logarithm property. For the given return loss RL = 6, we get R = 10^(-6/20) = 0.501. The transmission coefficient will be T = 1 –
R = 1-0.501 = 0.498.