Explanation
In optical communication, diode laser is used to generate analog signals or digital pulses for transmission through optical fibres. The advantage of diode lasers is their small size and low power input.
TV signals (frequency greater than 30 MHz) cannot be propagated through sky wave propagation.
Above critical frequency, an electromagnetic wave penetratates the ionosphere and is not reflected by it.
A is wrong. Frequency more than critical one can’t be transmitted.
Waves having the range of wavelength from 30 km to 30 cm are know as short waves. These waves are used for radio transmission and for general communication purpose to a longer distance from ionosphere. Ionosphere is the outermost region of atmosphere extending from height of 80 km to 400 km approximately, above the surface of earth. Therefore, both the assertion and reason are true and reason is the correct explanation of assertion.
The electrical conductivity of earth’s atmosphere increases with height so assertion is false.
When high energy particles enter in earth’s atmosphere they ionise the gases present in atmosphere. Also as we go up, the air thins out gradually and air pressure decreases.
The electromagnetic waves of shorter wavelength do not suffer much diffraction from the obstacles of earth’s atmosphere so they can travel long distance.
Also, shorter the wavelength, shorter is the velocity of wave propagation.
Both Assertion and Reason are true and Reason is the correct explanation of Assertion. (For more detail, refer theory).
As the distance increases, TV signals become weaker. So Assertion is true. The power transmitted from TV transmitter is inversely proportional to the square of the distance of the receiver. That’s why Reason is false.
Microwaves have got good directional properties. Due to it, the microwaves can be directed as beam signals in a particular direction, much better than radio waves, because microwaves do not bend around the corners of any obstacle coming in their way.
The remote sensing is done through a satellite. A remote sensing satellite flies in a polar orbit at an altitude of 918 km, around the earth, in such away that it passes over a given location on the earth at the same local time.
The electronic reproduction of a document at a distance plane is known as FAX. Modulation and demodulation is done by modem.
A dish antenna is a directional antenna because it can transmit.
Assertion is wrong because optical communication is preferred over microwave communication as optical communication can provide large number of channels and bandwidths and information carrying capacity is directly proportional to band width. Reason is also wrong
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