# Antennas Questions and Answers – Radio Wave Propagation – Structure of Ionosphere

This set of Antennas Multiple Choice Questions & Answers (MCQs) focuses on “Radio Wave Propagation – Structure of Ionosphere”.

1. At what height the Ionosphere lies above the earth surface?
a) 70-400km
b) 2-15km
c) 20-70km
d) Above 400km

Explanation: Troposphere is the lowest layer in the atmosphere ranging up to 15km. stratosphere lies at 50 to 90km and from 70- 400km ionosphere. Above 400km is the outer atmosphere.

2. Which of the following is the nearest Ionospheric layer to the earth surface?
a) D layer
b) E layer
c) F1 layer
d) F2 layer

Explanation: D layer is present at 70km from the earth surface and is the nearest layer to earth surface. E layer lies at 110km, f1 layer at 220km and F2 at 250 to 400km. Based on the density of ions different layers are present in this layer.

3. Which of the following layer disappears during night time in ionosphere?
a) D layer
b) E- layer
c) F1 layer
d) F2 layer

Explanation: During night time D layer disappears and F1, F2 layers combine together to form an F layer. D layer is present at 70km from the earth surface and is the nearest layer to earth surface. E layer lies at 110km, f1 layer at 220km and F2 at 250 to 400km.

4. Which of the following is called as Kennelly Heaviside layer?
a) E layer
b) F1 layer
c) F2 layer
d) D layer

Explanation: E layer is called as Kennelly Heaviside layer and F layer is called as Appleton layer. E layer lies at 110km, f1 layer at 220km and F2 at 250 to 400km.

5. In which of the following layers the electron density is high?
a) E layer
b) F1 layer
c) F2 layer
d) D layer

Explanation: The electron /ion density increases with the increase in height in ionosphere. F2 layer has 3×105 to 2×106 electron density . F2 layer = 2×105 to 4.5×105
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6. Which of the following follows Chapman’s law of variation?
a) D layer
b) F1 layer
c) F2 layer
d) Both F1 and F2 layer

Explanation: Only F1 layer follows the Chapman’s law of variation where F1 region behaves like an E-region. F1 layer is formed by the ionization of O2 atoms. F2 layer does not follow Chapman’s law of variation.

7. Which of the following regions are present in the night time?
a) D and E layers
b) E and F layers
c) F1 and F2 layers
d) D and F layers

Explanation: During night time D layer is not present. F1 and F2 layers get combined to form an F layer during night time. So E and F layers are present at night time.

8. Which of the following layer is used for long distance sky wave propagation during night hours?
a) F layer
b) E layer
c) D layer
d) All layers can be used

Explanation: F layer is the top layer in the ionosphere and is also present at the night time. So it is used for the long distance sky wave propagation and also its ionization density is high. D layer is not present during night hours.

9. Which of the following is formed by the ionization of UV and corpuscular radiations?
a) E layer
b) F1 layer
c) F2 layer
d) D layer

Explanation: F2 layer is formed by the ionization of the UV, x-rays and corpuscular radiations. F1 is formed by the ionization of O2 atoms. F layer is the top layer in the ionosphere and has highest electron density. D layer is due to photo ionization of O2 atoms at first level.

10. Which of the following layer is known as absorption layer for short waves?
a) E layer
b) F1 layer
c) F2 layer
d) D layer

Explanation: D layer is also known as absorption layer for short wave signal at HF. It reflects signals up to VLF and LF. Its absorption increases with solar activity.

11. Which of the following layer is known as F layer?
a) Appleton layer
b) Kennelly Heaviside layer
c) Absorption layer
d) Sir Appleton

Explanation: E layer is called as Kennelly Heaviside layer and F layer is called as Appleton layer. D layer is also known as absorption layer for short wave signal at HF.

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