The World Communicates:1.1 Recall two essential properties that distinguish electromagnetic waves from all other waves.1) Electromagnetic waves do not require a medium to travel through - they can travel through a vacuum. They are caused by electric and magnetic fields oscillating together but perpendicular to each other so that the electromagnetic wave moves in a direction perpendicular to both of the fields [this is caused by accelerating charges, whereas other waves rely on vibrations].2) All electromagnetic waves travel at the speed of light - 3.0 x 108 ms-1. Based on the formula v=fΛ, we can see that since v is a constant, then as the frequency increases, the wavelen ...view middle of the document...
1.4 Identify the methods of detection for gamma rays, X-rays, ultraviolet radiation, visible light, infra-red [heat] radiation, microwaves, radar, radio and TV-waves.Gamma Rays: Can be detected by Geiger countersX-rays: Can be detected by photographic film and special semiconductor detectors (in CAT scans)UV rays: Certain crystals will fluoresce (emit light at one wavelength when excited by radiation of a shorter wavelength) when they absorb UV.Visible light can be detected by the retina of the eye or photographic film. IR Radiation: Can be detected by our skin, thermometers and thermistors, as well as special kinds of photographic film used to detect sources of heat, and "night vision goggles".Microwaves: Can be detected using an antenna or detecting diode because the oscillating electric field vector produces an electric current in conducting materials.Radar (RAdio Detection And Ranging): These are short pulses of microwaves that can be detected using "speed cameras" or "speed guns".Radio waves: Can be detected using radio receivers that are connected to aerials, or by tuning into a particular frequency using a radio.TV-Waves: Can be detected using an antenna.2.1 Summarise information in a table or flowchart to identify the waves involved in the transfer of energy during the use of a mobile phone.2.2 Identify the electromagnetic bands and their frequencies used in communication.2.3 Identify the problems produced by the limited range of the electromagnetic spectrum for communication purposes.The greatest problem with long-distance communication is that the signals decrease in strength the further they are from the source (refer to the Inverse Square law - I ∝ 1/d2). This decrease in the strength of the signal or light is known as attenuation.Often, repeater or booster stations are required to amplify the signals sent in long-distance communication. Also, electromagnetic waves can be sent out as a very large strength signal to reduce the effects of attenuation. For very weak signals, the receiver may collect a signal over a large area and focus the signal to increase its strength.Microwave transmissions also have their range affected by atmospheric conditions, such as the moisture content of the air. Regular boosts to microwave signals and more sensitive receivers may be needed to receive short-wavelength microwaves.2.4 Explain how radio waves can be transmitted around the Earth.★See Figure 2.4.1 - Radio waves and the Ionosphere* Short wave radio waves are reflected off the ionosphere allowing short wave communications over long distances.* Medium wavelength radio waves pass straight through the ionosphere and are only good for "line of sight" communications.* Long wavelength radio waves are refracted off the ionosphere and can be used to communicate beyond the horizon.2.5 Discuss why most countries' governments place restrictions on the use of the limited range of the electromagnetic spectrum used in communications.3.1 Recall th...
