# Physics Questions and Answers – Communication Systems – Propagation of Electromagnetic Waves

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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Communication Systems – Propagation of Electromagnetic Waves”.

1. The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to which of the following?
a) h1/2
b) h
c) h3/2
d) h2

Explanation: The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to h1/2.
d = √2Rh.
d ∝ h1/2.

2. In communication with help of antenna if the height is doubled, then the range covered which was initially r would become what?
a) √2r
b) 3r
c) 4r
d) 5r

Explanation: Initial range, r = √2Rh.
When the height of the antenna is doubled,
r’ = √2R × 2h = √2r.

3. Identify the layer where ozone is present.
a) Troposphere
b) Stratosphere
c) Ionosphere
d) Mesosphere

Explanation: The ozone layer is present in the stratosphere. The ozone layer blocks the harmful ultraviolet radiation from reaching us. For this ultraviolet radiation, the wavelength is considered to be 3 × 10-7 m.
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4. Which of the following statements is wrong?
a) Ground wave propagation can be sustained at frequencies 500 kHz to 1500kHz
b) Satellite communication is useful for the frequencies above 30 MHz
c) Space wave propagation takes place through tropospheric space
d) Skywave propagation is useful in the range of 30 to 40 MHz

Explanation: Skywave propagation is useful for radio-waves of frequencies ranging from 2 MHz to 30 MHz. Higher frequencies than this value cannot be reflected by the ionosphere. All the other statements are correct.

5. What is the refractive index of the ionosphere?
a) Zero
b) More than one
c) Less than one
d) One

Explanation: Ionosphere is the uppermost layer of the earth’s atmosphere. The ionosphere has a very low density. The refractive index of the ionosphere is less than one.
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6. The biological importance of the ozone layer is to stop the greenhouse effect.
a) True
b) False

Explanation: No, this statement is false. The ozone layer stops the harmful ultraviolet radiation. It acts as a filter for harmful Ultraviolet radiation from the sun, thereby protecting the life on earth. It is a greenhouse gas.

7. Identify a suitable frequency for skywave propagation.
a) Upto 2 MHz
b) From 2 MHz to 30 MHz
c) From 2 MHz to 50 MHz
d) From 2 MHz to 80 MHz

Explanation: Skywave propagation is useful for radiowaves of frequency from 2 MHz to 30 MHz. Frequencies that are higher than 30 MHz cannot be reflected by the ionosphere.

8. What is the maximum distance upto which the TV transmission can be received, if the TV tower has a height of 220 m?
a) 37.75 km
b) 20 km
c) 59.3 km
d) 40.55 km

Explanation: d = √2Rh.
d = √2 × 220 × 8 × 106
d = 59329.58m ≈ 59330 m
d = 59.3 km.

9. What is the physical significance of the Ozone layer in the atmosphere?
b) Stops greenhouse effect
c) Stops increase in temperature of the atmosphere
d) Absorbs pollutant gases

Explanation: The ozone layer stops ultraviolet radiation. It acts as a filter against the harmful Ultraviolet radiation from the sun from reaching the living being on earth, thereby protecting the life on earth. This is the significance of the ozone layer.

10. The phase difference between space current and capacitive displacement current is 0 rad, when radio waves undergo the ionosphere.
a) True
b) False

Explanation: Yes, this is a true statement. The phase difference between space current and capacitive displacement current is zero. This current will generate a magnetic flux and if we are distant from the capacitor, it’ll be perpendicular to every other.

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