The Electro magnetic spectrum.

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The Electro magnetic spectrum.

By Steve Wyers 11cu

Radio Waves

Radio waves are made by various types of transmitter, depending on the wavelength. They are also given off by stars, sparks and lightning, which is why you hear interference on your radio in a thunderstorm. Radio waves are the lowest frequencies in the electromagnetic spectrum, and are used mainly for communications.

Radio waves are divided into:-

Long Wave, around 1~2 km in wavelength. The radio station "Atlantic 252" broadcasts here.

Medium Wave, around 100m in wavelength, used by BBC Radio 5 and other "AM" stations.

VHF, which stands for "Very High Frequency" and has wavelengths of around 2m. This is where you find stereo "FM" radio stations, such as "Galaxy 101" and "GWR FM". Further up the VHF band are civilian aircraft and taxis.

UHF stands for "Ultra High Frequency", and has wavelengths of less than a metre. It's used for Police radio communications, military aircraft radios and television transmissions.

Large doses of radio waves are believed to cause cancer, leukaemia and other disorders. Some people claim that the very low frequency field from overhead power cables near their homes has affected their health.


Microwaves are basically extremely high frequency radio waves, and are made by various types of transmitter. In a mobile phone, they're made by a transmitter chip and an antenna, in a microwave oven they're made by a "magnetron". Their wavelength is usually a couple of centimetres. Stars also give off microwaves. Microwaves cause water and fat molecules to vibrate, which makes the substances hot. Thus we can use microwaves to cook many types of food.

Mobile phones use microwaves, as they can be generated by a small antenna, which means that the phone doesn't need to be very big. The drawback is that, being small, they can't put out much power, and they also need a line of sight to the transmitter. This means that mobile phone companies need to have many transmitter towers if they're going to attract customers. Microwaves are also used by traffic speed cameras, and for radar, which is used by aircraft, ships and weather forcasters.

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The most common type of radar works by sending out bursts of microwaves, detecting the "echoes" coming back from the objects they hit, and using the time it takes for the echoes to come back to work out how far away the object is.

Prolonged exposure to microwaves is known to cause "cataracts" in your eyes, which is a clouding of the lens, preventing you from seeing clearly (if at all!) So don't make a habit of pressing your face against the microwave oven door to see if your food's ready!

Recent research indicates that microwaves from mobile phones can ...

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The language used by the candidate is often a little colloquial, which is great if the target audience is A-level students, but if this is supposed to be a piece of coursework, then formal language would be more appropriate. There is little issue with spelling and grammar, and for the most part punctuation is used in an acceptable manner. However, s/he does get a bit carried away with the use of exclamation marks, which should be avoided when writing an essay. Overall this is a good quality essay, it is informative, and the candidate clearly shows their knowledge of the subject. In addition the candidate has undergone independent research and indicates their interest in their subject.

The candidate shows a good level of understanding and goes into suitable depth when discussing each of the electromagnetic waves. S/he attempts to give additional information for each and goes beyond the subject knowledge required at this level. To achieve a higher grade, the candidate could have explored topics beyond the main essay question, for example they could have gone on to discuss polarisation. This links together nicely as EM waves are transverse waves and only transverse waves can be can be polarised. This level of analysis indicates the candidate’s breadth of knowledge and again illustrates an interest in their subject. Unfortunately the candidate fails to conclude this piece of work, a conclusion is necessary in an essay, it allows you to draw your work to a close and end on a suitable point. Without a conclusion the essay just stops and the reader can often be left feeling confused. A good conclusion summarises your key points and includes personal opinions on the essay topic. I understand that this can be difficult in Science, but it doesn’t need to be long, and it is good practice to have a conclusive paragraph.

Although the candidate discusses all of the electromagnetic waves, the essay just focuses on the main body of information and there is no introduction. Having an introduction is crucial, it sets the tone for the whole essay, it should summarise what you plan to look at and provide a context for your essay. It gives you a chance to catch the readers attention and indicate what you plan to discuss. However the candidate gives a fairly explicit response, s/he mentions uses for each of the EM waves as well as how they are formed. There is also evidence of independent research, a good of example of this is when the candidate discusses in detail the various types of wavelengths of radio waves and how they are used. This shows knowledge beyond that expected for this level of qualification, therefore shows the candidate’s interest and makes the essay more enjoyable for the reader. In addition the candidate attempts to engage with the reader, by making the odd joke and asking questions, again this makes the essay more enjoyable to read, although it’s best to keep this to a minimum or you risk sounding too informal. The candidate has made a very good attempt at discussing the electromagnetic waves, however they fail to mention the properties of all electromagnetic waves, such as the fact that they can travel through a vacuum this is because they are transverse waves (which means they oscillate at right angles to their direction of propagation) and they all travel at the speed of light.