Contains the full lesson along with a supporting toolkit, including teachers’ notes.
Radios and TVs pick up and process radio waves, i.e., electromagnetic waves typically ranging in frequency from 30 Hz to 30 GHz. Such broadcasts require high power transmitters. Most of the RTE radio transmitters operate at 200,000 watts (i.e. 200 kW) while the power of some local radio transmitters may be as low as 10 watts.
In Ireland (as in most countries) a person must obtain a licence for radio transmission. The type of licence depends on the application (mobile phone, amateur radio, air traffi c services etc.). The licence specifi es the maximum power and the frequency ranges or ‘bands’.
However, no licence is required for certain transmissions that we take for granted today. For instance, a mobile phone must be able to transmit radio signals as well as receive them. Mobile phones operate in specific radio frequency bands and their power is less than 0.4 W.
A smart phone may also have WiFi capability, that is, it uses a specified communications protocol and transmits radio signals at low power (generally less than 0.1 W). WiFi therefore has a short range ― typically less than 100 metres.
What are electromagnetic waves?
We take light for granted. At the flick of a switch we can turn on an electric lamp. The shape of shadows lead us to think that something is coming from the lamp and it seems to travel in straight lines. We can reflect light with a mirror and refract it with a lens. In 1678 Christiaan Huygens explained the properties of light in terms of waves of some sort. In 1690 Isaac Newton tried to explain the properties of light in terms of little particles or ‘corpuscles’ as he called them. However, around 1804 Thomas Young demonstrated diffraction and interference of light — properties that are characteristic of waves. The wave theory of light was then universally accepted. But nobody knew what was actually waving.
In 1831 Michael Faraday discovered electromagnetic induction, i.e the generation of electricity using a magnet and a conductor. Faraday thought that light might have electrical or magnetic properties and after years of trial and error he was eventually successful. He published his findings the following year (1845). This was a remarkable discovery. Indeed, many people today would not expect light to be affected by a magnet.
Its remit covers all kinds of transmission networks including: