The Electromagnetic Spectrum

The Electromagnetic Spectrum

1. The Discovery of Infrared

   • William Herschel put dark coloured filters on his telescope to help him observe the sun safely. He notices that different colours heated his telescope to different extents, causing hi to wonder if different colours of light contained different amounts of heat.
     • To test this, he used a prism to split the light into different colours, and put a thermometer in each colour. He also put a thermometer just beyond the red, and found that it gave the highest temperature. He called this Infrared raiation.
   • Johann Ritter found out about Herschel's discovery and decided that there must be invisible light beyond the blue as well. Silver Chloride was known to turn black more quickly in violet light, so Ritter showed that that the silver chloride turned black even quicker just beyond the blue. He called this Ultraviolet.

2. The Electromagnetic Specrum

   • Electromagnetic waves can travel without any particles to vibrate on, so they can travel through vacuums such as space. All electromagnetic waves travel at 300 000 km/s, which is the fastest speed anything can travel at.
     • The colour of visible light depends on its wavelength. If the wavelength is longer than that of red light, the human eye cannot see it. These waves have lower frequencies and the ones with shorter wavelengths have higher frequencies.
       • Gamma Rays- Used for radiotherapy and to detect cancers.However gamma rays can casue cancer.
       • X-Rays- X-rays can also cause cancers. X-ray scanners are used in medical scanners and security scanners to view what's in people's luggage.
       • Ultra-Violet- Fluorescent materials absorb UV radiation which can be used to detect if bank notes are real or not. UV radiation can also be used to sterilise medical equipment and food. UV radiation can however cause cataracts and skin cancer (melanoma)
       • Visible Light- can be used in bank note security, photography, lighting, photocopiers, scanners and man other everyday appliances.
       • Infrared- Is used for thermal imaging in CCTV cameras. IR waves are used in remote controls. The signals are sent down optical fibres for the TV or internet too. Toasters use IR for heat too.IR radiation can burn us.
       • Microwaves- Microwaves carry mobile phone signals, TV and satellite signals. They are also used in microwaves.Microwaves heat water, so could burn us.
       • Radiowaves- Widely used for communications and broadasting. They are used for TV signals and WiFi signals.

3. Ionising Radiation

   • Gamma rays can cause cancer by mutating a cell's DNA, this is because gamma rays are ionising radiation. This means that gamma rays can remove electrons from atoms to create ions. Ions are very reactive so if DNA cells are ionic, they will perform chemical reactions which cause mutations to the DNA. More exposure to gamma rays can also destroy the cell.
   • Radium naturally emits gamma rays all the time- it is radioactive. Not all radioactive elements emit gamma rays, some emit alpha particles and other beta particles.
     • Alpha and Beta particles are not electromagnetic radiation, they are particles of matter which are emitted with lots of kinetic energy which can ionise atoms.