1. Noadswood Science, 2011

2. EM & Communications  To understand how EM waves are used in communications Monday, August 25, 2014

3. Anagrams Solve the following anagrams: - Leetcmroanegitc murtsepc Drraenif Eeavwlnhgt Biisvle iltgh Magma Sary Qerenufcy Sary-X Leetcmroanegitc vwea Pamtildeu Zerth

4. Anagrams Solve the following anagrams: - Leetcmroanegitc murtsepc Drraenif Eeavwlnhgt Biisvle iltgh Magma Sary Qerenufcy Sary-X Leetcmroanegitc vwea Pamtildeu Zerth Electromagnetic spectrum Infrared Wavelength Visible light Gamma rays Frequency X-rays Electromagnetic wave Amplitude Hertz

5. EM Spectrum  Each type of radiation shown in the EM spectrum has a different wavelength, a different frequency and different uses  Visible light, microwaves and radio waves are the main EM spectrum wavelengths used for communications…

6. Radio Waves  Radio waves are used for communications – there are 3 types: - Short wave (3’000 – 30’000 kHz) only travel short distances but are very clear, e.g. FM Medium wave (300 kHz – 3 MHz) travel further than short wave, but are not as clear Long wave (>3 MHz) travel a very long way but are less defined

7. Optical Fibres (Visible Light)  Optical fibres can carry information coded in light or infrared signals – they can carry more information than an ordinary cable of the same diameter  Information such as computer data and telephone calls can be converted into electrical signals – this information can also be converted into either visible light signals or infrared signals, and transmitted by optical fibres  Optical fibres can carry more information than an ordinary cable of the same thickness – the signals in optical fibres do not weaken as much over long distances as the signals in ordinary cables

8. Optical Fibres  An optical fibre is a thin rod of high-quality glass (very little light is absorbed by the glass)  Light getting in at one end undergoes repeated total internal reflection, even when the fibre is bent, and emerges at the other end

9. Optical Fibres  Light getting in at one end undergoes repeated total internal reflection, even when the fibre is bent, and emerges at the other end  The critical angle for glass is about 42°  Diamond’s have a critical angle of 24° – this is why they sparkle so much, due to many internal reflections

10. Total Internal Reflection  Total internal reflection occurs when light is coming out of something dense, such as glass, water or perspex  If the angle is shallow enough the ray will not come out at all, but it reflects back into the material – this is total internal reflection

11. Total Internal Reflection  Angle of incidence is less than critical angle  Most of the light passes through the air, but a little bit of it is internally reflected

12. Total Internal Reflection  Angle of incidence = critical angle  The emerging ray comes out along the surface, with quite a lot of internal reflection

13. Total Internal Reflection  Angle of incidence is greater than the critical angle  No light comes out as it is all internally reflected (total internal reflection)

14. Optical Fibres - Uses  Optical communications have several advantages over electrical signals in wires: - The signal does not need boosting as often A cable of the same diameter can carry much more information The signals cannot be tapped into, or suffer interference from electrical sources  Normally no light would be lost at each reflection, however some light is lost due to imperfections in the surface, so boosters are needed every few km

15. Endoscopes  Endoscopes are used to look inside people – they are a narrow bunch of optical fibres with a lens system at each end (with another set of optical fibres to carry light down inside)  The image is displayed on a monitor, meaning operations can be undertaken without the need to cut large holes in the patient

16. Phones  How does a phone work – does it send sound up into space?!  Watch the demo of the mobile phone in a vacuum

17. Microwaves  Microwaves are used by satellites because they can pass through the Earth’s atmosphere – they are used for mobile phone networks and satellite TV