Physics - Communication with Transverse Waves (AQA Syllabus A)

One of the topics studied in GCSE Science is mechanical and electromagnetic waves. This is one of six quizzes on that particular subject and it looks specifically at using transverse electromagnetic waves for communication.

We know that there are two types of wave - transverse waves and longitudinal waves. Radio waves, microwaves, infrared, visible light, ultraviolet light, X-rays and gamma rays are all transverse waves. They are also all members of the electromagnetic spectrum and some of them can be used for communication. For the exam you should know some typical examples of how and where they are used, and any associated hazards.

One difficulty with using these electromagnetic waves for communication is that they travel in straight lines. This can cause problems because the surface of the Earth is curved. For the longer waves, like radio, this is not a massive issue because these waves can be reflected and they also diffract. Diffraction is the spreading out of a wave when it passes through a gap or around an object. The gap or object needs to be about the same size or smaller than the wavelength for diffraction to occur.

Radio waves can travel long distances because they can be reflected round the curvature of the Earth. They reflect off the ionosphere (a layer of the Earth's atmosphere) and off the surface of the Earth itself. Each time a wave is reflected it loses a little energy. This means that radio signals get weaker the further you are from the transmitter. It is for that reason that repeater stations are built which boost the signal strength and quality.

Radio waves can also travel round corners because of diffraction and can reach people in the bottom of valleys. It works because hills are comparable in size to the wavelength of radio waves. Diffraction allows radio signals to reach people who are not in direct line with the transmitter. The deeper and narrower the valley, the more difficult it is for them to receive a radio signal that is not coming from directly above.

As any owner of a mobile telephone will know, there are places where you can't get a signal. This is because they work using microwave technology. Microwaves have a much shorter wavelength than radio waves and so don't diffract as easily. They are also blocked more easily than radio waves which is why sometimes you need to move around a building or go outside to find the best signal.

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1. Which type of electromagnetic radiation travels the slowest?
All electromagnetic radiation travels at the same speed - the speed of light. The exact figure depends on what it is passing through and it is fastest in a vacuum
2. Why do mobile telephone users need to be in line of sight with a transmitter to get a signal?
Firstly, you need to know that microwaves are used for mobile telephone communication. Waves can only be diffracted (travel round corners) if the object they are going round or the gap through which they are passing is comparable in size to their wavelength. Since their wavelengths are less than 1 m, microwaves are not diffracted sufficiently by large objects like hills to reach people not directly in line with the mast
3. Which of the following is not a disadvantage of wireless communication?
Wireless communication can be used on almost any scale, from communication with satellites in deep space to a wireless network in the home
4. Which type of electromagnetic radiation can be reflected by the ionosphere, a layer of charged particles in the Earth's atmosphere?
It is the shorter radio wavelengths that reflect the best
5. Which of the following members of the electromagnetic spectrum has the highest frequency?
This form of electromagnetic wave cannot be used for communication because it carries too much energy and is harmful to living things
6. Which of the following members of the electromagnetic spectrum has the longest wavelength?
The waves used by radio stations usually have wavelengths of between 1 m and 1 km
7. Why do some people object to mobile telephone masts being erected near their homes?
There is concern that microwave radiation from mobile phones and masts may be harmful to health. This is not accepted by everybody because the strength and intensity of the microwaves transmitted from mobile telephone towers is too low to damage tissues by heating and is not ionising radiation which means it not likely to cause cancer
8. Why are microwaves used for communicating with satellites?
There are certain wavelengths of microwave that can pass through the atmosphere without being refracted
9. Which of the following is used in remote control devices for TV's, radios and similar appliances?
It is effective over short distances but cannot be used for long distance communication through the atmosphere
10. Which of the following is not a way that infrared radiation is used to transmit or receive information?
For security lights the transmitter is a person's body. All objects above the temperature of absolute zero emit (give out) infrared radiation

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