Question

Find the mismatch
A) Sky wave communication: Frequency up to 30 MHz
B) Line – of – sight communication: Frequency greater than 40 MHz
C) Mobile telephony: Frequency range 800 – 950 MHz
D) Facsimile: Static document
E) Ground wave propagation: Frequency less than a few MHz

Answer 1

Hint:- These are the electromagnetic waves which play their particular role in different fields. To find this mismatch, find the frequency of the waves mentioned in the question as their respective frequencies are written.

Complete step by step answer:
The waves in the question come under the electromagnetic spectrum as it is the range of frequencies of electromagnetic radiation and their respective wavelengths.

In the question, we have to find which way of communication does not match with the frequency written. So, we need to know about those waves or means of communication.

-The propagation of radio waves reflecting or refracting back towards the earth from the electrically charged layer of upper atmosphere is called Sky wave communication. When the frequency of the wave is above 30 MHz then, it can penetrate the ionosphere and will not return back to the earth’s surface, so the frequency of this type of communication is up to 30 MHz.

-The type of communication which can transmit and receive data only when transmitter and receiver are in view of each without any obstacles in between them is said to be line – of – sight communication. It works when the frequencies are above 40 MHz.

-Mobile telephony is the wireless service which provides telephone services in the mobiles which makes us move anywhere. Mobile communication uses 2G, 3G, 4G etc. for communications. So, the frequency used 2G network is 900 MHz to 1800 MHz and 3G networks use 2100 MHz frequency and this increases by the type of network.

Hence, from the above, we can conclude that mobile telephony communications are the one which mismatch with its frequency in the question as it uses frequency starting from 900 MHz.

Therefore, the correct option is (C).

Note: When there are low frequencies the radio waves can travel as ground waves which follow the contour of earth due to diffraction and at frequency from 1 to 30 MHz, the communication is known as Sky wave communication and therefore above 40 MHz, the way of communication is known as line of sight communication as there are no obstacles in between the receiver and transmitter.