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  1. ELECTROMAGNETIC SPECTRUM Name: ________________ Class: _________________ Index: ________________

  2. At the end of the topic you should be able to… • state that all electromagnetic waves are transverse waves that travel with the same high speed in vacuo and state the magnitude of this speed • describe the main components of the electromagnetic spectrum • discuss the role of the following components in the stated applications: • radiowaves in radio and television communication • microwaves in satellite television and microwave oven • infra-red waves in infra-red remote controllers and intruder alarms • light in optical fibres for medical uses and telecommunications • ultra-violet in sunbeds, and sterilisation • X-rays in radiological and engineering applications • Gamma rays in medical treatment • describe the effects of absorbing electromagnetic waves, e.g. heating, ionisation and damage to living cells and tissue

  3. Electromagnetic Spectrum

  4. Properties • An electromagnetic wave is produced by the simultaneous vibration of electric and magnetic fields. • All electromagnetic waves • transfer energy from one place to another • are transverse waves • can travel through vacuum. They DO NOT require any medium to travel from one point to another. • travel through a vacuum at the speed of 3 x 108 ms-1. • obey wave properties like reflection and refraction. • carry no electrical charge as they are neither positively nor negatively charged. • obey the wave equation: v = f.

  5. If electromagnetic waves travel in vacuum, then for the wave equation v = f v = c, where c is the symbol for the speed of light in vacuum  c = f  3.0 x 108 = f • Their frequencies do not change when they travel from one medium to another. (e.g.. From water to glass). This is because their frequency ƒ depends only on the source of the wave. Only their speeds and wavelengths change from one medium to another.

  6. Electromagnetic spectrum Components of electromagnetic spectrum long wavelength short wavelength Several km < 10-12 m high frequency low frequency Speed in a vacuum is constant c = 3 x 108 m s-1 “Ronald McDonald Is Very Ugly eXcept Gary”

  7. Applications of electromagnetic spectrum • For each component, you need to know • Range of wavelength • Its uses • Any harmful effects (The higher the frequency, the larger the amount of energy) • Source • Detector

  8. Radio wave • has wavelength of 10-1 to 105 m • Can move around obstacles • is used in radio communication and television transmission over long distances (LW, MW, SW, VHF, UHF). Radio telescope. • source: TV and radio transmitters detector: aerials of TV and radio receivers/antenna Television transmission is made possible with the use of VHF and UHF radio waves

  9. Microwave • has wavelength of 10-3 to 10-1 m (0.001 m to 0.1m) • is used in satellite communication and transmission, radar systems and microwave cooking/microwave oven • travels in straight line without losing much of its energy • source: electronic devices (eg. cavity magnetron in microwaves) detector: microwave receivers speed-monitoring radar satellite station

  10. Infrared radiation • is the radiation beyond the red end of the visible spectrum • has wavelength of 10-7 to 10-3 m • is used in remote control devices, intruder alarms, infra-red photography and radiant heaters • is emitted by hot objects • source: warm bodies detector: special photographic films, blackened thermometers and thermocouples an infra-red photograph

  11. Visible light • can be seen by human eye • has wavelength of 4 x 10-7 to 7 x 10-7 m • is used in optical fibres, medical usage, telecommunications, chemical spectral analysis and photosynthesis, endoscopy. Lasers for medical, industrial and surveying use. • source: hot bodies, lasers and sun detector: eyes, photographic film and photocells laser surgery

  12. Ultraviolet radiation • has wavelength of 10-8 to 10-7 m • stimulates our bodies to produce vitamin D • Can cause tanning, overexposure can lead to skin cancer • is used in sunbeds, fluorescent tubes, sterilisation, forgery detection and fluorescence in washing powders • source: sun, mercury vapour and lamps detector: photographic film, fluorescent screens, dyes and photocells overexposure to UV radiation can cause skin cancer

  13. X ray • has wavelength of 10-13 to 10-8 m • is penetrating and can cause damage to tissues and organisms • Doctors, nurses and people working in X-ray environment have to wear protective clothing to shield themselves from X ray • is used in medical and dental diagnostic tools and engineering applications. Check for flaws/cracks in metals. Detect artwork forgery. Airport scanners. Crystal structure analysis. • source: x-ray tubes detector: photographic film and fluorescent screens x-ray photograph of hand

  14. Gamma ray (HIGHEST ENERGY!!!!, HIGHEST FREQUENCY) • has wavelength of 10-14 to 10-10 m • is penetrating and can cause damage to living tissues and organisms • is used in treatment of cancer (gamma knives – sharp beam of gamma ray) and checking of welds, under controlled situations. Sterilising equipment. • source: cosmic rays, radioactive substances and nuclear reaction detector: Geiger-Müller counters (GM tube), bubble/cloud chambers and photographic film

  15. Effects of EM Waves on Cells and Tissue • Exposure to electromagnetic radiation primarily causes heating effects such as the pain of sunburn or skin cancer. However, over-exposure may result in harmful effects such as pain of sunburn or skin cancer. • EM waves can be classified as either ionising radiation or non-ionising radiation: • Ionising radiations are extremely high frequency EM waves which include X-rays and gamma rays. They have enough photon energy to produce ionisation (a process where one or more electrons are removed from a neutral atom by radiation). It is a harmful process leading to destruction or modification of living cells. • Non-ionising radiations are the part of the EM spectrum which has photon energies too weak to produce ionisation. Examples are ultra-violet, visible light, infra-red radiation, microwave and radio wave.

  16. Memory aid (song) for Electromagnetic Spectrum

  17. consist of are with speed in vacuum Electromagnetic waves Applications Radio and television communication Satellite television and telephone Home electrical appliances, remote controls and intruder alarms Optical fibres in medical usage and telecommuncation Sunbeds, fluorescent tubes and sterilisation Medical use and engineering applications Medical treatment Components Radio waves Microwaves Infra-red waves . Light Ultra-violet . X-rays Gamma rays Transverse waves c = 3 x 108 m s-1

  18. Reference: