P1e(ii) Cooking and Communicating Using Waves You will learn about: Uses of Microwaves Dangers of Mobile Phones and Masts

Microwaves for Communication Risks? Some people are worried about the increasing use of mobile phones. The image on the left shows the infrared activity after a 15 minute mobile phone call. It is clearly seen that the tissues around the brain are significantly heated. Some people are worried about diseases and cancer that may be related to this. A person naturally emits about 60 Joules of energy each second. About 20 Joules of that energy passes into the head. A mobile phone emits about ¼ or ½ of a Joule of energy each second. This is a relatively small amount when compared to what the body already emits. So is it right that people should be worried? As of yet there is no scientific proof that mobile phones cause brain related diseases but in time, when scientists understand brain development better, that may change. ?

Line of Sight A transmitter is usually up high on top of a microwave mast. This is because the transmitter needs to be in line of sight with the receiver. If it is not then the signal will not be received. Obstructions such as tall buildings or mountains can prevent microwave signals reaching a receiver. Sometimes the Earth’s curvature prevents a transmitted microwave to reach a receiver. Microwaves can pass through our atmosphere. They can reach a satellite in space. This satellite receives the signal, amplifies it and re-transmits it to locations on Earth the original transmitter could not. REMEMBER: Microwaves can pass through our atmosphere

Line of Sight Issues? Telecom Tower in London stands tall above most of London. This ensures that each satellite is in line of sight with as many receivers as possible. But how would you feel if you went to a school nearby that was in direct line of sight? Would you be worried about the amount of microwave exposure? Lots of studies have been conducted but there is no simple conclusion. This is why it is important for scientists to work together and repeat results. This way they can be sure that their findings are correct. Currently, health advisors suggest that mobile phones be limited in usage and that hands free kits be used whenever possible. They are worried that in the future some findings may actually confirm that mobile phones are a danger to people, particularly children and teenagers as their brains have not yet developed fully.

Microwave Properties RECALL: Microwaves cover a long bandwidth. The shortest are about 1mm and the longest about 30cm. Cooking uses shorter wavelengths whereas those used for communication are much longer. We learnt previously that the shorter the wavelength the lower the amount of energy. This means that mobile phones use microwaves with lower energy values than those used for cooking. The earth’s atmosphere is made up of several layers. Each layer is a different density. Microwaves are refracted when they pass through a different dense layer. Within the atmospheric layers exists an atmospheric duct – a layer where the density is just right that microwaves do not pass through but refract and follow the curvature of the Earth. Fog and adverse weather conditions can cause an atmospheric duct too. Microwaves do not diffract by very much. Look at the image below. They are not able to diffract around hills or tall buildings like radio waves can. This causes signal loss and explain why mobile phone reception can be poor in some locations. Microwaves diffract very little so cannot reach the house on the other side like radio waves can. Microwave signal loss also occurs when two or more signals overlap. They then interfere with one another. In this image you can see mobile phones and an over interfering with the laptop computer signal.

Questions 1.If you used a mobile phone how much energy would enter your head during a five minute phone call? 2.Why does the Government suggest texting instead of talking on a mobile phone? 3.Why are microwaves positioned on very tall buildings? 4.Do you think mobile phone masts should be placed near an infant school playground? Why? 5.Why do you think cities have more mobile phone masts than the countryside?

Questions 1.If you used a mobile phone how much energy would enter your head during a five minute phone call? Use ¼ Joule per second. Five minutes is 300 seconds. So ¼ x 300 = 75J. If use ½ Joule per second then ½ x 300 = 150J. Answer is between 75J and 150J. 2.Why does the Government suggest texting instead of talking on a mobile phone? Reduce the amount of microwaves entering the head and perhaps causing brain damage. 3.Why are microwaves positioned on very tall buildings? Better line of sight to receivers. 4.Do you think mobile phone masts should be placed near an infant school playground? Why? Answer should be no! Children’s brains have not yet developed so microwaves could alter that development. Although the scientific evidence is not conclusive it is better to be safe than sorry. 5.Why do you think cities have more mobile phone masts than the countryside? Cities have more obstacles like tall buildings than the countryside. There is more chance of getting a line of sight between transmitter and receiver if more mobile phone masts are present.