P13 electromagnetic waves

• electromagnetic waves transfer energy without transferring matter
• light travels at 300,000 km/s
• the EM spectrum is radio, microwaves, infrared, visible, ultraviolet, x-ray and gamma
• the EM is in order of decreasing wavelength and increasing frequency
• radio waves are used to transmit sound and images over long distances
• the human eye can only detect visible light
• all electromagnetic waves travel at 3x10^8 m/s in a vacuum
• electromagnetic waves obey the properties of waves
• white light contains all the colours of the visible light spectrum
• infrared radiation is used for carrying signals from remote control handsets and inside optical fibres and in thermal imaging cameras
• microwaves are used to carry satellite TV and mobile phone calls
• mobile phone radiation is microwave and radio waves at near microwave frequencies
• different types of electromagnetic radiation are hazardous in different ways
• microwaves and radio waves can heat up the internal parts of peoples bodies
• infrared radiation can cause burns to skin
• dispersion

  when white light passes through a prism, it is split into it's component colours because the different frequencies/wavelengths refract by different amounts
• radio waves of different frequencies are used for different purposes because the wavelength affects

  • how far they can travel
  • how much they spread
  • how much information they can carry
• carrier waves

  waves that are used to carry information by varying their amplitude
• optical fibres

  thin transparent fibres that are used to transmit communication signals by light and radiation
• radio waves are emitted from a transmitter aerial when an alternating current is connected and they have the same frequency as the voltage
• higher frequency radio waves can give better quality sound and video or more channels but have a shorter range as they are absorbed more by the atmosphere and they disperse less so are more likely to be stopped by buildings
• information carried by radio waves is called a signal
• mobile phones use microwaves as they are generated by a small antena so they phone doesn't have to be big
• optical fibres can carry more information than microwaves as light and infrared have higher frequencies
• x-rays are produced in x-ray tubes
• x-rays are ionising radiation which can develop photographic film
• x-rays can cause cells to mutate and cause cancer
• to minimise risk to radiographers

  • wear lead apron
  • stand behind lead/glass wall
  • signs to stop people entering the room
• gamma rays are produced by radioactive substances in an unstable nuclei
• gamma rays can kill or mutate cells
• gamma rays can kill cancer but also cause cells to mutate leading to cancer